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Volume 272, Number 43, Issue of October 24, 1997 pp. 27230-27238
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

Thyroid Na⁺/I Symporter
MECHANISM, STOICHIOMETRY, AND SPECIFICITY^*

(Received for publication, May 22, 1997, and in revised form, August 20, 1997)

Sepehr Eskandari ^§, Donald D. F. Loo , Ge Dai ^¶, Orlie Levy ^¶, Ernest M. Wright and Nancy Carrasco ^¶

From the  Department of Physiology, UCLA School of Medicine, Los Angeles, California 90095-1751 and the ^¶ Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461

ABSTRACT

INTRODUCTION

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION

FOOTNOTES

ACKNOWLEDGEMENTS

REFERENCES

ABSTRACT

The rat thyroid Na⁺/I symporter (NIS) was expressed in Xenopus laevis oocytes and characterized using electrophysiological, tracer uptake, and electron microscopic methods. NIS activity was found to be electrogenic and Na⁺-dependent (Na⁺  Li⁺  H⁺). The apparent affinity constants for Na⁺ and I were 28 ± 3 mM and 33 ± 9 µM, respectively. Stoichiometry of Na⁺/anion cotransport was 2:1. NIS was capable of transporting a wide variety of anions (I, ClO₃, SCN, SeCN, NO₃, Br, BF₄, IO₄, BrO₃, but perchlorate (ClO₄) was not transported. In the absence of anion substrate, NIS exhibited a Na⁺-dependent leak current (~35% of maximum substrate-induced current) with an apparent Na⁺ affinity of 74 ± 14 mM and a Hill coefficient (n) of 1. In response to step voltage changes, NIS exhibited current transients that relaxed with a time constant of 8-14 ms. Presteady-state charge movements (integral of the current transients) versus voltage relations obey a Boltzmann relation. The voltage for half-maximal charge translocation (V_0.5) was 15 ± 3 mV, and the apparent valence of the movable charge was 1. Total charge was insensitive to [Na⁺]_o, but V_0.5 shifted to more negative potentials as [Na⁺]_o was reduced. NIS charge movements are attributed to the conformational changes of the empty transporter within the membrane electric field. The turnover rate of NIS was 22 s¹ in the Na⁺ uniport mode and 36 s¹ in the Na⁺/I cotransport mode. Transporter density in the plasma membrane was determined using freeze-fracture electron microscopy. Expression of NIS in oocytes led to a ~2.5-fold increase in the density of plasma membrane protoplasmic face intramembrane particles. On the basis of the kinetic results, we propose an ordered simultaneous transport mechanism in which the binding of Na⁺ to NIS occurs first.

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INTRODUCTION

It is now firmly established that active accumulation of iodide (I) by the thyroid gland epithelium, previously referred to as the "iodide pump" or "iodide trap," is a Na⁺-dependent secondary active transport process mediated by the Na⁺/I symporter (NIS),¹ an integral plasma membrane protein of the basolateral membrane of the thyroid gland follicular cells. Iodide transport into the thyroid gland has attracted substantial scientific and clinical interest due to the importance of I in the biosynthesis of thyroid hormones triiodothyronine and tetraiodothyronine, and to the significance of NIS in the diagnosis and treatment of thyroid disorders (1). A cDNA clone encoding NIS has recently been isolated, sequenced, and expressed in Xenopus laevis oocytes (2). Oocytes injected with NIS cRNA exhibit a 700-fold increase in perchlorate-sensitive I uptake.

This study reports a comprehensive characterization of rat NIS function expressed in X. laevis oocytes. NIS activity is Na⁺-dependent and electrogenic, and the stoichiometry of cotransport is 2 Na⁺:1 anion. Kinetics of transport as a function of external Na⁺ and substrate concentration suggest an ordered binding of Na⁺ and substrate to the transporter in which binding of Na⁺ occurs first. Substrate selectivity experiments show that a variety of anions are transported into the cell via NIS. However, perchlorate, the most potent known inhibitor of NIS, is not transported. Measurements of charge movements associated with NIS conformational changes, and substrate-uncoupled Na⁺-dependent leak currents of NIS have provided insight into the nature of Na⁺/I cotransport. Combined data from electrophysiological measurements and freeze fracture electron microscopy suggest that NIS may be multimeric in its functional form.

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EXPERIMENTAL PROCEDURES

NIS cRNA (50 ng) was microinjected into stage V-VI X. laevis oocytes (2, 3), and the oocytes were maintained in Barth's solution at 18 °C until used for experiments. Oocytes were superfused with buffers containing (in mM): 100-0 NaCl, 0-100 choline chloride, 2 KCl, 1 CaCl₂, 1 MgCl₂, 10 HEPES, pH 7.5. Chloride was replaced with gluconate in Cl-free solutions. For cation selectivity experiments, NaCl was replaced with choline chloride or LiCl at pH 7.5 or choline chloride at pH 5.0 (adjusted with MES).

Electrophysiological Measurements

Electrophysiological recordings were done using the two-microelectrode voltage clamp technique at 22 ± 1 °C (4). To obtain current/voltage (I/V) or charge/voltage (Q/V) relations, the pulse protocol (pCLAMP, Axon Instruments) consisted of 100-ms voltage steps from a holding potential (V_h) of 50 mV to a series of test voltages (V_m) from +50 to 150 mV in 20 mV decrements. Currents from three sweeps were averaged, low-pass filtered at 500 Hz, and sampled at 100 µs.

Tracer Uptake under Voltage Clamp

Uptake of ¹²⁵I (15 µCi/mol; Amersham Corp.) was determined in NIS cRNA-injected oocytes in the presence of 100 mM Na⁺ and 50 µM I. V_h was 90 mV, and substrate-evoked inward currents were recorded for 10 min. Total inward charge movement was determined by integration of the current with time. At the end of the recording period, oocytes were washed with ice-cold choline buffer, solubilized with 10% sodium dodecyl sulfate, and assayed for ¹²⁵I content. ²²Na⁺ (2.5 µCi/mol; DuPont) uptake was determined in the presence of 30 mM Na⁺ (choline, 70 mM) and in the presence or absence of 5 mM anionic substrate.

Freeze-Fracture Electron Microscopy

After maximum charge (Q_max) measurements (see below), oocytes were fixed as described previously (5). Images of P (protoplasmic) and E (exoplasmic) fracture faces where enlarged to a final magnification of × 75,000 and intramembrane particles (IMP) from both the P and E fracture faces where counted from known areas of the membrane. Total number of transporters per oocyte was estimated by determining the total area of the oocyte plasma membrane from the total plasma membrane capacitance (5), and assuming a membrane specific capacitance of 1 microfarads/cm². The diameter of the P face IMPs was measured directly from the negative using a profile projector (Nikon, model 6c).

Data Analysis

Substrate-evoked currents were obtained as the difference in steady-state current measured in the absence and presence of substrate and were fitted to,

(Eq. 1)

where I is the evoked current, I_max^S is the maximum current, S is the substrate (anion or Na⁺), K_0.5^S is the substrate concentration at half-maximal current, and n is the Hill coefficient. To obtain the presteady-state currents, total currents were fitted to Equation 2, and transporter-mediated transients were determined by subtracting the capacitive and steady-state components,

(Eq. 2)

where I_total is the total current, I_Cm is the initial membrane capacitive current, ₁ is the time constant of I_Cm, I_PS is the initial presteady-state current, ₂ is the time constant of I_PS, and I_SS is the steady-state current. Q/V relations were obtained by integration of the presteady-state current with time for various voltages and were fitted to the Boltzmann relation,

(Eq. 3)

where the total charge Q_max = Q_dep  Q_hyp (Q_dep and Q_hyp represent Q at depolarizing and hyperpolarizing limits), z is the apparent valence of the moveable charge, V_m is the membrane voltage during the pulse, V_0.5 is the membrane voltage at which half of the total charge has moved, F is Faraday's constant, R is the gas constant, and T is the absolute temperature. Unless otherwise indicated, results obtained from experiments on individual oocytes are presented, but all experiments were repeated on at least three oocytes from different donor frogs. Data fits were performed using Clampfit (Axon Instruments) or Sigma Plot (Jandel Scientific). Errors are reported as S.E. of the estimate obtained from the fit or as S.E. of the mean obtained from data from several oocytes.

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RESULTS

Steady-state Currents

Electrogenicity of NIS is shown in Fig. 1. Addition of 500 µM I to the bathing medium caused an inward current of ~400 nA in an oocyte expressing NIS. ClO₄ (500 µM), a specific blocker of I transport by the Na⁺/I symporter, abolished the I-evoked inward current. Fig. 2 shows typical I/V relationships in a NIS-expressing oocyte before (A) and after (B) addition of I (500 µM) to the bath. In the absence of substrate (Fig. 2A), after the initial fast capacitive transient ( = 0.5 ms), NIS exhibited slower presteady-state currents that relaxed to a steady state with a time constant of 8-14 ms (see also Fig. 8). Presteady-state currents were apparently abolished by the addition of I (Fig. 2B). Addition of I led to a depolarization of the membrane, the magnitude of which depended on the level of NIS expression, and ranged from 5 to 50 mV (not shown).

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Fig. 1. Electrogenicity of the Na⁺/I symporter. Current was recorded from a NIS cRNA-injected oocyte at V_h = 50 mV, and the oocyte was superfused with the solutions indicated in the top panel. Base line was established in the Na⁺ buffer (100 mM NaCl). Addition of I (500 µM) to the bath caused a large inward current. ClO₄ (500 µM) completely inhibited the I-evoked inward current. Perchlorate, by itself, does not generate an inward current.

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Fig. 2. Voltage and concentration dependence of I-induced inward currents. Current traces were obtained from a NIS cRNA-injected oocyte before (A) and after (B) addition of I (500 µM) to the perfusion solution. The pulse protocol is shown. In A the presteady-state currents associated with NIS are evident (see also Fig. 8). B, addition of I (500 µM) apparently eliminated the presteady-state currents and induced an inward current. Dotted traces show current at the holding potential and emphasize the difference caused by the addition of I. C, net I-evoked inward current was taken as the difference between the steady-state current in the presence (1-100 µM) and absence of I and plotted as a function of V_m.

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Fig. 8. Presteady-state currents: charge movement. A, typical current traces of a NIS-expressing oocyte in response to voltage steps from a V_h of 50 mV in the absence of substrate. The pulse protocol was as shown in Fig. 2. The current trace for each voltage step was fitted to Equation 2. ₁, the time constant of the membrane capacitive current was ~0.5 ms for the largest voltage step (100 mV). The dotted line represents zero current at V_h. B, carrier-mediated transient currents. The traces in this figure were obtained by subtracting the capacitive and steady-state components (obtained from Equation 2) from the total current (A) and are plotted 1.5 ms after the onset of the voltage step. C, Q/V relation of charge movements. Q was determined by time integration of the carrier-mediated transient currents (B) for the ON (Q_ON; ) and OFF (Q_OFF; ) transients. The smooth line is a single Boltzmann fit to the average of Q_ON and Q_OFF according to Equation 3. Q_max = 12 ± 0.6 nanocoulombs, z = 0.9 ± 0.1, V_0.5 = 17 ± 2 mV. D, /V relation of the charge transfer.  was determined from the fit of the total currents in A to Equation 2. _ON/V () was bell-shaped and the smooth line is a Gaussian fit to _ON. _max was 14 ms, and the voltage at which _max was observed (V_max) was 54 ± 2 mV. _OFF was voltage-independent and is shown for +50 mV (). The time constants of the membrane capacitive currents for the ON () and OFF () responses are also shown (~0.5 ms).

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The magnitude of the I-induced inward current increased with hyperpolarizing potentials, but did not saturate within this voltage range (150 to 10 mV; Fig. 2C). Iodide-induced inward current was concentration-dependent and saturable. At each voltage, the net I-induced current was plotted as a function of [I] and fitted to Equation 1 (n = 1). At 50 mV, the apparent affinity constant of NIS for I (K_0.5^I) ranged from 15 to 75 µM and averaged 33 ± 9 µM (N = 7; Fig. 3A).

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Fig. 3. Kinetics of iodide transport. A, I-induced current as a function of external I concentration (V_m = 50 mV). The curve is the fit to Equation 1 (n = 1). B, K_0.5^I as a function of V_m. C, I_max^I as a function of V_m. Error bars are the S.E. of the estimates.

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The apparent affinity constant of NIS for iodide (K_0.5^I) was relatively voltage-independent between 150 and 50 mV and increased at potentials more positive than 50 mV (Fig. 3B). Maximal iodide-induced current (I_max^I) increased in a superlinear fashion as the membrane was driven toward more negative potentials and did not saturate in this voltage range (Fig. 3C).

Anion Selectivity

Fig. 4 shows the relative substrate selectivity of NIS. In this experiment, current was monitored as anions were added (500 µM) to the perfusion solution. The best transported substrates were I, ClO₃, SCN, SeCN, and NO₃. SCN was transported to a significant extent, but ClO₄ was not transported at all. The transported anions did not induce an appreciable inward current in H₂O-injected oocytes from the same batch (see below). NO₂, HCO₃, acetate, succinate, SO₃², CO₃², S₂O₃², and P₂O₄⁴ were not transported (not shown).

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Fig. 4. Substrate selectivity of the Na⁺/I symporter. Inward currents induced by various anions (500 µM) were recorded at V_m = 50 mV. Currents were normalized with respect to the current generated by I. I-induced current in the absence of Cl did not differ from that in the presence of 100 mM Cl (not shown). Other anions tested which did not induce a detectable inward current were: NO₂, HCO₃, SO₃², CO₃², S₂O₃², P₂O₄⁴, acetate, and succinate. Data are reported as mean ± S.E. (N = 3).

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The relative apparent affinity of NIS for anions (Table I) were: I (1.00)  SeCN (0.87) > SCN (0.34) > ClO₃ (0.12) > NO₃ (0.04). The relative I_max values (I_max^I = 1) ranged from 0.8 to 1.5 (Table I). The voltage dependence of K_0.5 and I_max was the same for all of the above anions (not shown).

Table I. Kinetics of anion cotransport Imaxsubstrate values have been normalized to ImaxI obtained from the same oocyte from which the substrate-induced current was obtained. Values are mean ± S.E. from at least three oocytes. Reported values are for Vm = 50 mV. Anion K0.5 Imax µM I 33  ± 9 1.00 SeCN 38  ± 15 0.8  ± 0.1 SCN 96  ± 9 0.8  ± 0.2 ClO3 277  ± 20 1.0  ± 0.2 NO3 739  ± 223 1.5  ± 0.2

Inhibition of Iodide-induced Inward Current

ClO₄ completely blocked the current generated by 50 µM I, with an apparent half-inhibition constant (K_i^ClO₄) of 1.8 ± 0.4 µM (N = 4). K_i^ReO₄ was also very low (3.2 ± 0.4 µM; N = 5), but this inhibitor could only block the I-induced current by 86 ± 3%. This could be due to the fact that at high concentrations (500 µM), ReO₄ itself can induce a very small inward current (Fig. 4). BF₄ and IO₄ (500 µM) reduced the I-evoked (50 µM) inward currents by 74 ± 10% and 21 ± 6%, respectively (N = 3).

In some control (non-injected) oocytes, I induced a small but detectable inward current, which was prominent at high iodide concentrations (>500 µM) and at depolarizing membrane potentials (10 to +50 mV). These iodide currents were insensitive to perchlorate. Of the anions that are readily transported by NIS (I, ClO₃, SCN, SeCN, and NO₃), only ClO₃ did not exhibit this behavior. Therefore, we chose to use ClO₃ as a model anion for further kinetic studies.

Cation Selectivity

When Na⁺ in the perfusion solution was isotonically replaced with choline, no I-induced (500 µM) inward current was observed at either pH 7.5 or 5.0. Li⁺, however, was able to drive transport at a reduced level. At 150 mV, the Li⁺/I current was 10-20% of the Na⁺/I current (not shown).

Na⁺- and ClO₃ Activation of Inward Currents

In Fig. 5A, inward currents induced by 0.25, 1, and 5 mM ClO₃ are plotted as a function of external Na⁺ concentration ([Na⁺]_o). At each substrate concentration, inward currents saturated with increasing [Na⁺]_o. The Hill coefficient for Na⁺ was ~2 regardless of the substrate concentration and V_m; at [ClO₃] = 1 mM and V_m = 50 mV, n = 2.2 ± 0.1. I_max^Na+ increased with increasing substrate concentration (Fig. 5B) and the apparent affinity of NIS for Na⁺ increased as [ClO₃] was increased (Fig. 5C). At 50 mV, at [ClO₃] = 0.25, 1, and 5 mM, K_0.5^Na+ was 57 ± 7, 39 ± 3, and 28 ± 3 mM, respectively.

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Fig. 5. Na⁺ activation of currents. A, inward currents as a function of [Na⁺]_o are plotted at 0.25, 1, and 5 mM [ClO₃]. Smooth lines are fits of the data to Equation 1. As the substrate concentration was increased, I_max^Na+ increased (B) and K_0.5^Na+ decreased (C), while the Na⁺ Hill coefficient did not vary significantly (2). All data were obtained from the same oocyte. Reported values are for V_m = 50 mV. Error bars are the S.E. of the estimates.

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Examination of substrate kinetics at different [Na⁺]_o (Fig. 6A) showed that although I_max^ClO₃ remained constant as [Na⁺]_o was lowered (Fig. 6B), the apparent affinity of NIS for substrate decreased dramatically (Fig. 6C); K_0.5^ClO₃ was 271 ± 5 µM at 100 mM [Na⁺]_o and 1671 ± 263 µM at 20 mM [Na⁺]_o.

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Fig. 6. Substrate activation of currents. A, inward currents as a function of ClO₃ concentration are plotted at 20, 40, and 100 mM [Na⁺]_o. Smooth lines are fits of the data to Equation 1 (n = 1). B, I_max^ClO₃ as a function of [Na⁺]_o. C, K_0.5^ClO₃ as a function of [Na⁺]_o. All data were obtained from the same oocyte. Reported values are for V_m = 50 mV. Error bars are the S.E. of the estimates.

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Voltage Dependence of Kinetic Parameters

Fig. 7A shows the voltage-dependence of K_0.5^ClO₃ at various [Na⁺]_o. Regardless of [Na⁺]_o, K_0.5^ClO₃ approached 150 µM at hyperpolarizing limits. At less negative membrane potentials K_0.5^ClO₃ varied greatly depending on [Na⁺]_o. As with K_0.5^ClO₃, K_0.5^Na+ varied with voltage and with the concentration of cosubstrate (Fig. 7B).

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Fig. 7. Voltage dependence of the apparent sodium and substrate affinity. A, K_0.5^ClO₃ as a function of V_m at 20, 40, 55, 70, and 100 mM [Na⁺]_o. B, K_0.5^Na+ as a function of V_m at 0.25 and 1 mM [ClO₃].

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Presteady-state Charge Movement

In the absence of substrate, NIS cRNA-injected oocytes exhibited presteady-state current transients in response to step changes in V_m (Figs. 2A and 8A). These current transients were not observed in control H₂O-injected oocytes (see Ref. 3). Fitting of the current traces (both ON and OFF; Fig. 8A) to Equation 2 resolved three components: (i) a fast component ( ~0.5 ms) due to oocyte membrane capacitive currents (also seen in control oocytes); (ii) a second slower component ( 8-14 ms), which was the NIS-mediated current; and (iii) a steady-state current due to "leak" pathways in NIS and the membrane. To obtain the carrier-mediated transients, the membrane capacitive and steady-state components were subtracted from the total current (Fig. 8B). At each clamped voltage, integration of the carrier-mediated currents (Fig. 8B) with time yielded the charge (Q) moved by NIS within the membrane electric field. Fig. 8C shows a Q/V relationship for NIS. Q_ON and Q_OFF were equal and opposite in sign and reversed at V_h (50 mV). The Q/V curve fitted a single Boltzmann relation (Equation 3) with a V_0.5 of 15 ± 3 mV and a z of 0.9 ± 0.1 (N = 8). The time constant of the slow current transient was voltage-dependent for the ON response. _ON/V was bell-shaped and ranged from 8 to 14 ms with its maximum value at ~55 mV (V_max) (Fig. 8D). _OFF was voltage-independent at ~10 ms (; Fig. 8D).

Fig. 9A shows Q/V curves at 0-100 mM [Na⁺]_o. There was no loss in Q_max as [Na⁺]_o was reduced from 100-20 mM (Fig. 9B), but V_0.5 shifted from 17 mV at 100 mM [Na⁺]_o to 90 mV at 20 mM [Na⁺]_o (Fig. 9C). z was ~1 at all Na⁺ concentrations. The maximum value of the time constant of the relaxation currents (_max 14 ms) did not change as [Na⁺]_o was reduced (not shown), but V_max shifted from ~55 mV at 100 mM [Na⁺]_o to ~74 mV at 20 mM [Na⁺]_o (not shown).

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Fig. 9. Na⁺ dependence of the presteady-state currents. A, Q/V curves at various [Na⁺]_o (0-100 mM) in the absence of substrate. Smooth lines are Boltzmann fits to the experimental data as described in the legend to Fig. 8. For comparison, the curves have been normalized with respect to Q_dep at 100 mM [Na⁺]_o and shifted vertically such that all Q_dep values are aligned with Q_dep at [Na⁺]_o = 100 mM (see Refs. 4 and 25). B, Q_max as a function of [Na⁺]_o. C, as [Na⁺]_o was reduced, V_0.5 shifted to the left. The apparent valence of the moveable charge (z) (~1) and _max (~14 ms) did not change as [Na⁺]_o was reduced from 100 to 0 mM (not shown). Error bars are the S.E. of the estimates.

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Addition of either substrate or inhibitor led to a reduction in Q_max (Fig. 10A). As the concentration of substrate or inhibitor was increased, the decrease in Q_max followed a hyperbolic function (not shown). With ClO₃, 50 percent reduction in Q_max was reached at 586 ± 80 µM (N = 3). The ClO₃-induced reduction in Q_max was directly proportional to the steady-state ClO₃-induced inward current (Fig. 10B). At 50 and 150 mV, the slope of the plot I versus Q was 36 ± 2 s¹ and 61 ± 4 s¹, respectively.

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Fig. 10. Reduction in Q_max by substrate. A, Q/V relations in the absence () and presence () of 5 mM ClO₃. V_h = 50 mV. Smooth lines are Boltzmann fits of the data to Equation 3. The reduction in Q by ClO₃ was concentration-dependent and saturable with an apparent inhibition constant of 586 ± 80 µM (N = 3). B, the reduction in Q_max was directly proportional to the ClO₃-evoked steady-state inward current. At each [ClO₃], Q_max was determined from the Q/V relation and expressed as a percentage of Q_max in the absence of ClO₃. The slope (NIS turnover rate) was 36 ± 2 s¹ at 50 mV. At 150 mV, the turnover rate was 61 ± 4 s¹ (not shown).

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Na⁺-dependent Leak

In NIS-expressing oocytes, replacement of 100 mM choline chloride with NaCl caused an inward current that was much larger (>100 nA; Fig. 11A) than that seen in H₂O-injected oocytes (<20 nA at 50 mV). Addition of 500 µM I caused a further increase in the inward current. The Na⁺-dependent inward current, in the absence of substrate, is referred to as the NIS Na⁺ leak current. The Na⁺ leak current was saturable with increasing [Na⁺]_o. At 50 mV, the [Na⁺]_o at which the leak current was half-maximal (K_0.5^leak) was 74 ± 14 mM (N = 3; Fig. 11B), and the Hill coefficient was 0.9 ± 0.1 (N = 3). Control H₂O-injected oocytes exhibited inward Na⁺ currents that had a half-saturation constant of 9 ± 2 mM (N = 3). The magnitude of the leak current increased linearly with the level of expression, such that there was a direct linear correlation between the leak current and the substrate-induced current. At 150 mV, the plot of maximum leak current as a function of maximum ClO₃-induced current (I_max^leak versus I_max^ClO₃) yielded a slope of 0.34 ± 0.04 (N = 7; not shown).

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Fig. 11. Na⁺-dependent leak. A, Na⁺-dependent current in the absence and presence of substrate in a NIS-expressing oocyte. V_h = 50 mV. In the absence of substrate, Na⁺ induced an inward current in NIS-expressing oocytes, which was much larger than that seen in control oocytes. B, kinetics of the Na⁺-dependent inward leak current. The curve is the fit to Equation 1. The apparent Na⁺ affinity of the leak pathway (K_0.5^leak) was 74 ± 14 and the Na⁺ Hill coefficient was 0.9 ± 0.1 (N = 3). Control H₂O-injected oocytes exhibited an inward current (<20 nA at 50 mV) which saturated with increasing [Na⁺]_o with a half-saturation constant of 9 ± 2 mM (N = 3; not shown).

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Stoichiometry

Fig. 12A shows a current record from a NIS-expressing oocyte held at 90 mV and perfused with a solution containing I (100 mM Na⁺, 50 µM I, and 15 µCi/mol ¹²⁵I) for 10 min. Integration of the I-evoked inward current yielded the net positive charge that entered the oocyte during the recording period (shaded region). In the same oocyte, I uptake was measured by determination of ¹²⁵I content. A plot of the net inward charge versus I uptake from 10 oocytes revealed a linear relation with a slope of 0.76 ± 0.03 inward charge per iodide uptake (Fig. 12B). In Fig. 12C, inward charge is plotted as a function of Na⁺ uptake. Inward current was induced by 5 mM ClO₃ for 10 min in the presence of 30 mM Na⁺ and 2.5 µCi/mol ²²Na⁺. The slope of the line was 0.42 ± 0.04 inward charge per Na⁺ uptake (N = 6).

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Fig. 12. Stoichiometry of Na⁺/anion cotransport. A, I-induced current in a NIS-expressing oocyte superfused with 50 µM I in Na⁺ buffer ([Na⁺] = 100 mM and 15 µCi/mol ¹²⁵I) for 10 min. V_h was 90 mV for the entire experiment. Integration of the inward current with time represents the net positive charge that entered the oocyte (shaded region). The total charge in nanocoulombs, was converted to total positive charge in pmol using Faraday's constant. Iodide uptake was estimated by post-recording determination of oocyte ¹²⁵I content. B, I-induced current (inward positive charge) as a function of I uptake. The slope is 0.76 ± 0.03 charge/I (N = 10; ). The open circle () represents data from two oocytes which were incubated for 10 min in a solution that contained 100 mM choline instead of Na⁺, 50 µM I, and ¹²⁵I. This point represents ¹²⁵I uptake in NIS-expressing oocytes in the absence of Na⁺. No inward current was induced under this condition. When control H₂O-injected oocytes were incubated in 100 mM Na⁺, 50 µM I, and ¹²⁵I, the resulting data points were statistically indistinguishable from zero and on the graph would overlap with the open circle (not shown). C, ClO₃-induced current (inward positive charge) as a function of Na⁺ uptake. The slope is 0.42 ± 0.04 charge/Na⁺ (N = 7; ). [Na⁺] was 30 mM ([choline] = 70 mM), and [ClO₃] was 5 mM. The open circles represent Na⁺ uptake in the absence of substrate. The open square represents the mean Na⁺ uptake for three control H₂O-injected oocytes in 30 mM Na⁺ ([choline] = 70 mM), ²²Na⁺, and no substrate. The difference between the ²²Na⁺ uptake for NIS-expressing oocytes () and control oocytes () represents Na⁺ uptake through the leak pathway.

[View Larger Version of this Image (24K GIF file)]

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NIS Intramembrane Particles

Freeze-fracture electron micrographs of the P fracture face from the plasma membrane of a control H₂O-injected oocyte and an oocyte expressing NIS are shown in Fig. 13. In the control oocyte, the density of IMPs in the P face was 356 ± 69/µm² (mean ± S.D.; Fig. 13A). The endogenous intramembrane particles showed a relatively homogenous distribution with a mean diameter of 7.6 ± 1.2 nm (N = 875). Oocytes expressing NIS showed a ~2.5-fold increase in the density of P face particles to 887 ± 146/µm² (Fig. 13B). In contrast, the density of IMPs in the E face was not altered by expression of NIS (not shown; see Ref. 5). In addition, P face intramembrane particles of NIS-expressing oocytes showed a greater heterogeneity in size. Analysis of the diameter of P face IMPs (N = 856) in oocytes expressing NIS showed two prominent populations: one at 7.2 ± 0.5 nm corresponding to the endogenous particles and another at 9.0 ± 0.6 nm due to NIS particles. In the oocyte in Fig. 13B, Q_max was 18 nanocoulombs and the total number of transporters (N_NIS) in the plasma membrane was 3.5 × 10¹⁰. Q_max = N_NISZe, where Z is the valence of the moveable charge per NIS particle, and e is the electronic charge. Therefore, Z was estimated to be ~3 electronic charges.

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Fig. 13. Protoplasmic face freeze-fracture electron micrographs of a control and a NIS-expressing oocyte. The P face of a control H₂O-injected oocyte plasma membrane (A) showed IMPs at a density of 356 ± 69/µm². A total of 2130 IMPs were counted from 11 different regions of the P face (covering a total area of 6.3 µm²). In an oocyte expressing NIS (B), the density of IMPs in the P face increased to 887 ± 146/µm². A total of 1960 IMPs were counted from eight regions of the P face (total area = 2.2 µm²). The oocytes in A and B were from the same batch. Calibration bar: 0.1 µm.

[View Larger Version of this Image (136K GIF file)]

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DISCUSSION

General Properties of NIS

Cloning of the Na⁺/I symporter and its expression in X. laevis oocytes has made it possible to carry out a thorough functional characterization of this transporter. Iodide transport via NIS generates a net influx of positive charge (an inward current) that depolarizes the membrane. The inward current is Na⁺-dependent, stimulated by I, and coupled to Na⁺ and I influx. Uptake studies indicate that 2 Na⁺ ions are transported with one anion, resulting in inward movement of one positive charge. Previously, the electrogenic nature of the Na⁺/I symporter had been suggested in experiments using plasma membrane vesicles from hog thyroid (6).

The apparent affinity constant of NIS for I (33 ± 9 µM at 50 mV) is in general agreement with those obtained in uptake studies in NIS-expressing X. laevis oocytes (36 µM) (2), FRTL-5 cells (30 µM) (7), and membrane vesicles derived form porcine thyroid (5 µM) (6, 8). It is significant to note that the reported free iodide concentration in the mammalian plasma is 50-300 nM (1), while the K_0.5^I determined in this and other studies is in the low micromolar range. The apparent affinity constant of NIS for Na⁺ (28 ± 3 mM at 50 mV and saturating substrate) is also comparable with that found in other studies (~50 mM) (6, 9).

Anion Selectivity

In addition to I, a number of other anions are transported by NIS: I  SeCN > SCN > ClO₃ > NO₃. The only apparent common denominator for the well transported substrates is anionic monovalency. The closer the size of the monovalent anion to that of I, the better it is transported (10). No conclusion, however, can be drawn regarding the molecular geometry of a good substrate. Iodide is nearly spherical while SeCN and SCN are near-linear; ClO₃ has a trigonal pyramidal geometry; and NO₃ is planar. Regardless of the geometry of the anion, the qualitative similarity of transport kinetics of I, SeCN, SCN, ClO₃, and NO₃ suggests that their mechanism of transport may be the same.

Inhibition of Iodide Transport

A number of anions can significantly inhibit I transport. Most notable is ClO₄, the most potent known inhibitor of NIS (K_i^ClO₄ = 1.8 ± 0.4 µM). Previous reports suggested that ReO₄ (perrhenate) is transported into the thyroid (10). Our results show that ReO₄ is also a very potent blocker (K_i^ReO₄ = 3.2 ± 0.4 µM), but at high concentrations (>500 µM) it is transported via NIS to a very small extent (Fig. 4). ClO₄ and SCN were traditionally used as competitive inhibitors of I uptake in the thyroid gland, and both were believed to be transported via the Na⁺/I cotransport system (1, 11). In our system, SCN is transported, but perchlorate is not. That perchlorate is not transported by NIS is not unique to the Xenopus oocyte expression system as similar results have been obtained with rat NIS expressed in Chinese hamster ovary cells (12). Our data, however, cannot exclude electroneutral Na⁺/ClO₄ transport (1:1 coupling ratio).

Thus, anions that effectively interact with NIS can be subdivided into three groups: (i) anions that are readily transported; e.g. I, SeCN, SCN, ClO₃, and NO₃; (ii) anions that partially inhibit I transport, but are themselves transported to some extent; e.g. IO₄, BF₄, and ReO₄; and (iii) anions that completely inhibit transport; ClO₄. Although no conclusion can be drawn about the molecular commonality of the first group, anions belonging to the second and third groups all have a tetrahedral molecular geometry with an anionic volume very similar to that of I (13, 14).

The choroid plexus, salivary glands, lactating mammary glands, gastric mucosa, placenta, ciliary body of the eye, and kidney tubules have also been shown to possess a Na⁺-dependent I transport system (see Refs. 1 and 14). The anion selectivity of NIS found in this study (K_0.5 or K_i) was: ClO₄ > ReO₄ > I  SeCN > SCN > ClO₃ > NO₃. This is very similar to that in thyroid (10, 13) and choroid plexus (15), with the exception that in those tissues, SCN was found to interact with a higher apparent affinity than I.

Cation Selectivity

The specificity of Na⁺-dependent cotransporters for Na⁺ as the driving cation is not absolute. Proton can substitute for Na⁺ in the Na⁺/glucose cotransporter (SGLT1) (16) and the serotonin transporter (17). Sugar transport by SGLT1 is also driven by Li⁺ (18). Iodide transport through NIS was not driven by H⁺, but Li⁺ was able to drive transport at a reduced level (10-20% of Na⁺-driven transport). This is consistent with results on porcine thyroid plasma membrane vesicles (6).

Stoichiometry

Na⁺ activation of I influx in porcine thyroid plasma membrane vesicles revealed Na⁺ Hill coefficients of 1.6-1.8 (6, 8). Hill analysis of Na⁺ activation curves (e.g. Fig. 5A) provides an index of the number of Na⁺ ions necessary to activate the transport process (n = 2.2 ± 0.1), but does not determine the number of Na⁺ ions that actually enter the cell as a result of transporter activity. The actual stoichiometry can be inferred by simultaneous monitoring of inward charge and Na⁺ and substrate influx under voltage-clamp conditions. Measurement of Na⁺- and anion-evoked inward currents under voltage-clamp with determination of Na⁺ and anion uptake revealed that for every anion taken up, 0.76 ± 0.03 positive charge entered the cell and, conversely, for every Na⁺ taken up, 0.42 ± 0.04 positive charge entered the cell (Fig. 12). The stoichiometry obtained from the ratio is 1.8 ± 0.2 (0.76/0.42). This suggests a 2 Na⁺:1 anion stoichiometry.

Steady-state I/V Relationship

The I/V curves (Figs. 2C) and both I_max^I (Fig. 3C) and I_max^Na+ (not shown) increase in a linear or superlinear fashion with hyperpolarizing voltages with no evidence of saturation. Thus, in the voltage range tested (150 to 10 mV), there is at least one rate-limiting voltage-dependent step in the transport cycle (19). This behavior is unlike that of SGLT1 (3), which shows a saturation of I/V curves with voltage, but is similar to that of the Na⁺/myo-inositol cotransporter (SMIT) (20) and the taurine transporter (21).

Voltage Dependence of Kinetic Parameters

That negative membrane potentials increased the apparent affinity of NIS for Na⁺ is consistent with the presence of a Na⁺ well (19). Increased cation affinity with membrane hyperpolarization has been observed in other mammalian Na⁺-driven cotransporters, e.g. SGLT1 (3), SGLT2 (22), and SMIT (20), and in a mammalian proton-driven oligopeptide transporter (hPEPT1) (23). Further evidence for the existence of a Na⁺ well was provided by the fact that at hyperpolarizing potentials, K_0.5^ClO₃ was independent of [Na⁺]_o (Fig. 7A), indicating that a negative V_m could offset the effect of reduced [Na⁺]_o.

The apparent affinity for I was relatively insensitive to voltage at hyperpolarizing potentials, but exhibited a sharp voltage dependence at potentials more positive than 50 mV. It may seem counterintuitive that at negative membrane potentials, the apparent affinity for an anion is voltage-independent. One possibility is that the putative conformational change associated with Na⁺ binding to the transporter (see below) would position the I binding site at or beyond the membrane electric field/water interface such that, at hyperpolarized potentials, it no longer senses the membrane electric field. Alternatively, Na⁺ binding to the transporter induces a conformational change that creates a low access resistance path for I entry, and the voltage drop across such path may be very small to allow for detection of a voltage dependence of K_0.5^I.

Na⁺-dependent Leak

In the absence of substrate, there was a Na⁺-dependent inward current via NIS, which was ~35% of the current induced at saturating substrate concentration. Uptake studies also showed that, in the absence of substrate, there was increased Na⁺ influx in NIS-expressing oocytes (Fig. 12C). The apparent affinity constant for the Na⁺ leak (K_0.5^leak) was greater than twice the apparent affinity constant of the Na⁺/I transport pathway (K_0.5^Na+); at 50 mV, K_0.5^leak  75 mM, whereas K_0.5^Na+  30 mM. The Hill coefficient for Na⁺ activation of the leak current was 1. This implies that in the absence of substrate, NIS behaves as a Na⁺ uniporter, and may confer a resting Na⁺ conductance to the cell.

Presteady-state Charge Movements

In the absence of substrate and in response to step-changes in V_m, presteady-state currents are observed for NIS, as for other cloned cotransporters expressed in X. laevis oocytes; e.g. SGLT1 (4, 24), SGLT2 (22), hPEPT1 (23), SMIT (20), GABA transporter (GAT1) (25), and plant H⁺/hexose cotransporter (STP1) (26). Presteady-state currents represent charge translocations and provide clues about partial reactions in the transport cycle. Also similar to other cotransporters, NIS total charge translocation (Q_max) appears to decrease in the presence of substrate and/or inhibitor.

We observed no reduction in Q_max with decreasing [Na⁺]_o from 100-20 mM, and only a small decrease was seen in Q_max at [Na⁺]_o = 0 mM (Fig. 9B). This behavior is similar to that of SGLT2 (22), but unlike that of SGLT1 (24) and hPEPT1 (23), which show an apparent reduction in Q_max (~20%) as the external concentration of the driving cation (Na⁺ or H⁺) is reduced. At nominal zero external sodium, NIS Q_max appeared to be smaller, but this is most likely due to the large left-shift in V_0.5, which precludes us from obtaining a reliable Boltzmann fit in the voltage range tested. Therefore, charge movements in NIS are primarily due to the conformational changes of the empty transporter within the membrane electric field (shaded region in Fig. 14), but there may also be a minor contribution to the total charge due to Na⁺ binding/dissociation.

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Fig. 14. Schematic representation of Na⁺/I cotransport. In this scheme, one Na⁺ ion binds to the transporter first, which in the absence of substrate is able to cross the membrane via NIS in a Na⁺ uniport mode (CNa  CNa"; C, carrier). Release of Na⁺ into the cytoplasm is followed by the return of the empty binding site to complete the pathway (C"  C). The CNa₂  CNa₂" transition is not expected to contribute significantly to the leak current. The kinetic data suggest that Na⁺ binds to NIS before the anion, and the stoichiometric data provide strong evidence that the coupling ratio is 2 Na⁺:1 anion. In the presence of I, the complex CNa₂I is formed which undergoes a conformational change to expose the bound I and 2 Na⁺ ions to the interior of the cell (CNa₂I  CNa₂I"). Both Na⁺ ions and I are released into the cytoplasmic compartment, and the empty carrier undergoes another conformational change to expose the binding sites to the external solution again. Charge movement data suggest that Na⁺ binding/dissociation does not contribute greatly to the total observed charge. Thus, it is proposed that NIS charge movements arise primarily from conformational changes of the empty carrier (shaded region).

[View Larger Version of this Image (26K GIF file)]

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For a 10-fold reduction in [Na⁺]_o, V_0.5 shifted by ~100 mV to negative potentials, similar to that seen for other transporters (e.g. SGLT1, SGLT2, hPEPT1). This indicates that in the absence of I, Na⁺ can bind to NIS, and it is possible that the shift in V_0.5 is due to Na⁺ binding-induced conformational changes of NIS. Similar to other cotransporters, the apparent valence of the moveable charge for NIS is 1. Therefore, the basic features of charge translocation by NIS are similar to what has been reported for other cotransporters (see Table II in Ref. 24).

Substrate-coupled and Substrate-uncoupled Turnover Rate

Both I_max^substrate and I_max^leak are dependent on the number of transporters present in the plasma membrane. Q_max is an index of transporter density in the plasma membrane (see "NIS Intramembrane Particles"). NIS turnover rate was estimated using two different approaches. First, in several NIS-expressing oocytes, both Q_max (in the absence of substrate) and I_max (in the presence of saturating substrate) were measured. NIS turnover rate was then estimated from the slope of I_max versus Q_max plot; 37 ± 2 s¹ at 50 mV and 66 ± 4 s¹ at 150 mV (N = 18). These values are comparable with those found for other cotransporters (see Table I in Ref. 23). Second, in individual oocytes, Q_max was measured in the absence and presence of various concentrations of substrate, with simultaneous recording of the substrate-induced inward current. When substrate-induced inward current is plotted as a function of Q_max in the same oocyte, nearly identical turnover numbers result from the slope of the line; 36 ± 2 s¹ at 50 mV and 61 ± 4 s¹ at 150 mV (Fig. 10B). Nonetheless, both approaches underestimate maximum NIS turnover rate, since the I/V curve does not saturate in the voltage range tested (see Fig. 2C). The existence of a large leak pathway leads to a large turnover rate in the substrate-uncoupled (Na⁺ uniport) mode relative to that found for other cotransporters. In the absence of substrate and at 100 mM [Na⁺]_o, the substrate-uncoupled turnover rate for NIS is 22 ± 2 s¹ at 50 mV and 27 ± 2 s¹ at 150 mV (N = 7), whereas that for SGLT1 is less than 5 s¹ (27).

Mechanism of Na⁺/I Cotransport

The steady-state kinetic data point to an ordered, simultaneous transport mechanism in which Na⁺ binds first to the transporter followed by iodide (Fig. 14). This ordered mechanism was inferred from the observation that I_max^Na+ was dependent upon the substrate concentration (Fig. 5B), whereas I_max^ClO₃ was independent of [Na⁺]_o (Fig. 6B) indicating that binding of Na⁺ to the transporter occurs first (28). Thus, regardless of [Na⁺]_o, once Na⁺ is bound to the transporter, greater concentrations of substrate can drive transport to the same maximum velocity. Transport is simultaneous because decreases in the concentration of Na⁺ or substrate lead to decreases in the apparent affinity of the other (Figs. 5C and 6C) (29).

According to the scheme in Fig. 14, at physiological Na⁺ concentrations and membrane voltages, the Na⁺ binding site of NIS faces the extracellular solution with one bound Na⁺ ion (CNa). Reorientation of the transporter within the membrane exposes the bound Na⁺ to the intracellular compartment (CNa  CNa") followed by its release into the cytoplasm. Return of the empty Na⁺ binding site to the external solution completes the cycle (C"  C). This pathway constitutes the Na⁺ leak or Na⁺ uniport pathway and has a turnover rate of 22 s¹. In the presence of I, CNa₂I is formed which undergoes a transition resulting in the bound ions facing the cytoplasmic space (CNa₂I  CNa₂I"). Release of the bound ions is followed by the return of the empty carrier. This second pathway constitutes the Na⁺-dependent I transport pathway and has a turnover rate of 36 s¹.

NIS Intramembrane Particles

Expression of NIS in oocytes led to a ~2.5-fold increase in the density of intramembrane particles in the P face of the oolemma. This increase in the density of IMPs reflects the insertion of NIS particles into the membrane. Using the total number of transporters in the membrane obtained by freeze-fracture electron microscopy, and Q_max obtained electrophysiologically from the same oocyte, the valence of NIS moveable charges was estimated to be ~3 electronic charges per particle (Q_max = N_NISZe). This is in contrast with electrophysiological measurements, where a single Boltzmann fit of the Q/V curves predicts the apparent (effective) valence of the moveable charge of NIS to be 1. However, effective valence as measured electrophysiologically would only be equal to the actual moveable charge if, in response to a voltage jump, all of the moveable charge of NIS moved in one step (30). This is highly unlikely and the discrepancy between the two values is not surprising. A similar result has been reported for SGLT1 and the Shaker K⁺ channel (5).

The cloned cDNA for NIS codes for a 618 amino acid protein with a molecular weight of 65 kDa, and expression of NIS in X. laevis oocytes led to the appearance of 9-nm (diameter) particles. In comparison, the particles associated with the Shaker K⁺ channel (70 kDa) and the water channel, CHIP28 (28 kDa), in oocytes were 10.7 and 9.3 nm, respectively (5). There is strong evidence that Shaker K⁺ channel (31, 32) and CHIP28 (33) form functional homotetramers. Thus, based on these observations and the possible existence of a leucine-zipper motif in NIS (2), it is tempting to suggest that NIS may function as a multimeric protein.

Conclusion

From a mechanistic viewpoint, NIS steady-state and presteady-state kinetics are very similar to those of other cotransporters. This points to the possibility that, although the ionic nature of the substrate may vary (neutral, anionic, or cationic), the mechanism by which Na⁺-coupled transporters perform their function remains similar. This is substantiated by the fact that NIS belongs to the SGLT1 gene family and exhibits 25% amino acid identity with SGLT1. Subtle differences do exist and are related to the specific function performed by the transporter. Therefore, it is possible that a common ancestor gene existed which then upon divergence coded for different proteins able to couple various substrates to Na⁺ transport while preserving the general mechanistic aspects of the cotransport process (34).

FOOTNOTES

ACKNOWLEDGEMENTS

We gratefully thank Manoli Contreras for her excellent technical assistance with the oocytes; Jason Lam for cRNA preparation; Drs. A. Finkelstein, B. A. Hirayama, and G. A. Zampighi for their critical review of the manuscript; and Dr. B. Mackenzie for assistance with flux studies. Additional thanks go to Dr. G. A. Zampighi and M. Kreman for preparing the freeze-fracture micrographs.

REFERENCES

1. Carrasco, N. (1993) Biochim. Biophys. Acta 1154, 65-82 [Medline] [Order article via Infotrieve]
2. Dai, G., Levy, O., and Carrasco, N. (1996) Nature 379, 458-460 [CrossRef][Medline] [Order article via Infotrieve]
3. Parent, L., Supplisson, S., Loo, D. D. F., and Wright, E. M. (1992) J. Membr. Biol. 125, 49-62 [Medline] [Order article via Infotrieve]
4. Loo, D. D. F., Hazama, A., Supplisson, S., Turk, E., and Wright, E. M. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 5767-5771 [Abstract/Free Full Text]
5. Zampighi, G. A., Kreman, M., Boorer, K. J., Loo, D. D. F., Bezanilla, F., Chandy, G., Hall, J. E., and Wright, E. M. (1995) J. Membr. Biol. 148, 65-78 [Medline] [Order article via Infotrieve]
6. O'Neill, B., Magnolato, D., and Semenza, G. (1987) Biochim. Biophys. Acta 896, 263-274 [Medline] [Order article via Infotrieve]
7. Weiss, S. J., Philp, N. J., and Grollman, E. F. (1984) Endocrinology 114, 1108-1113 [Abstract/Free Full Text]
8. Nakamura, Y., Ohtaki, S., and Yamazaki, I. (1988) J. Biochem. (Tokyo) 104, 544-549 [Abstract/Free Full Text]
9. Kaminsky, S. M., Levy, O., Garry, M. T., and Carrasco, N. (1991) Eur. J. Biochem. 200, 203-207 [Medline] [Order article via Infotrieve]
10. Halmi, N. S. (1961) Vitam. Horm. 19, 133-163
11. Anbar, M., Guttmann, S., and Lewitus, Z. (1959) J. Appl. Radiat. Isot. 7, 87-96
12. Yoshida, A., Sasaki, N., Mori, A., Taniguchi, S., Mitani, Y., Ueta, Y., Hattori, K., Sato, R., Hisatome, I., Mori, T., Shigemasa, C., and Kosugi, S. (1997) Biochem. Biophys. Res. Commun. 231, 731-734 [CrossRef][Medline] [Order article via Infotrieve]
13. Wolf, J. (1964) Physiol. Rev. 44, 45-90 [Free Full Text]
14. Wright, E. M., and Diamond, J. M. (1977) Physiol. Rev. 57, 109-156 [Abstract/Free Full Text]
15. Wright, E. M. (1974) J. Physiol. (Lond.) 240, 535-566 [Abstract/Free Full Text]
16. Hirayama, B. A., Loo, D. D. F, and Wright, E. M. (1994) J. Biol. Chem. 269, 21407-21410 [Abstract/Free Full Text]
17. Cao, Y., Mager, S., and Lester, H. A. (1997) Biophys. J. 72, A407
18. Hirayama, B. A., Loo, D. D. F, and Wright, E. M. (1997) J. Biol. Chem. 272, 2110-2115 [Abstract/Free Full Text]
19. Lauger, P. (1991) Electrogenic Ion Pumps, Sinauer Associates, Inc., Sunderland, MA
20. Hager, K., Hazama, A., Kwon, H. M., Loo, D. D. F., Handler, J. S., and Wright, E. M. (1995) J. Membr. Biol. 143, 103-113 [Medline] [Order article via Infotrieve]
21. Loo, D. D. F., Hirsch, J. R., Sarkar, H. K., and Wright, E. M. (1996) FEBS Lett. 392, 250-254 [CrossRef][Medline] [Order article via Infotrieve]
22. Mackenzie, B., Loo, D. D. F., Panayotova-Heiermann, M., and Wright, E. M. (1996) J. Biol. Chem. 271, 32678-32683 [Abstract/Free Full Text]
23. Mackenzie, B., Loo, D. D. F., Fei, Y.-J., Liu, W., Ganapathy, V., Leibach, F. H., and Wright, E. M. (1996) J. Biol. Chem. 271, 5430-5437 [Abstract/Free Full Text]
24. Hazama, A., Loo, D. D. F., and Wright, E. M. (1997) J. Membr. Biol. 155, 175-186 [CrossRef][Medline] [Order article via Infotrieve]
25. Mager, S., Naeve, J., Quick, M., Labarca, C., Davidson, N., and Lester, H. A. (1993) Neuron 10, 177-188 [CrossRef][Medline] [Order article via Infotrieve]
26. Boorer, K. J., Loo, D. D. F., and Wright, E. M. (1994) J. Biol. Chem. 269, 20417-20424 [Abstract/Free Full Text]
27. Umbach, J. A., Coady, M. J., and Wright, E. M. (1990) Biophys. J. 57, 1217-1224 [Medline] [Order article via Infotrieve]
28. Segel, I. H. (1975) Enzyme Kinetics, John Wiley & Sons, Inc., New York
29. Jauch, P., and Lauger, P. (1986) J. Membr. Biol. 94, 117-127 [CrossRef][Medline] [Order article via Infotrieve]
30. Bezanilla, F., and Stefani, E. (1994) Annu. Rev. Biophys. Biomol. Struct. 23, 819-846 [Medline] [Order article via Infotrieve]
31. MacKinnon, R. (1991) Nature 350, 232-235 [CrossRef][Medline] [Order article via Infotrieve]
32. Schulteis, C. T., Nagaya, N., and Papazian, D. M. (1996) Biochemistry 35, 12133-12140 [CrossRef][Medline] [Order article via Infotrieve]
33. Verbavatz, J.-M., Brown, D., Sabolic, I., Valenti, G., Ausiello, D. A., van Hoek, A. N., Ma, T., and Verkman, A. S. (1993) J. Cell Biol. 123, 605-618 [Abstract/Free Full Text]
34. Turk, E., and Wright, E. M. (1997) J. Membr. Biol. 159, 1-20 [CrossRef][Medline] [Order article via Infotrieve]

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				S. Faham, A. Watanabe, G. M. Besserer, D. Cascio, A. Specht, B. A. Hirayama, E. M. Wright, and J. Abramson The Crystal Structure of a Sodium Galactose Transporter Reveals Mechanistic Insights into Na+/Sugar Symport Science, August 8, 2008; 321(5890): 810 - 814. [Abstract] [Full Text] [PDF]

				R. S. Fortunato, D. L. Ignacio, A. S. Padron, R. Pecanha, M. P. Marassi, D. Rosenthal, J. P. S. Werneck-de-Castro, and D. P Carvalho The effect of acute exercise session on thyroid hormone economy in rats J. Endocrinol., August 1, 2008; 198(2): 347 - 353. [Abstract] [Full Text] [PDF]

				M. D. Reed-Tsur, A. De la Vieja, C. S. Ginter, and N. Carrasco Molecular Characterization of V59E NIS, a Na+/I- Symporter Mutant that Causes Congenital I- Transport Defect Endocrinology, June 1, 2008; 149(6): 3077 - 3084. [Abstract] [Full Text] [PDF]

				N. Tran, L. Valentin-Blasini, B. C. Blount, C. G. McCuistion, M. S. Fenton, E. Gin, A. Salem, and J. M. Hershman Thyroid-stimulating hormone increases active transport of perchlorate into thyroid cells Am J Physiol Endocrinol Metab, April 1, 2008; 294(4): E802 - E806. [Abstract] [Full Text] [PDF]

				D. D. Vadysirisack, E. S.-W. Chen, Z. Zhang, M.-D. Tsai, G.-D. Chang, and S. M. Jhiang Identification of in Vivo Phosphorylation Sites and Their Functional Significance in the Sodium Iodide Symporter J. Biol. Chem., December 21, 2007; 282(51): 36820 - 36828. [Abstract] [Full Text] [PDF]

				O. Dohan, C. Portulano, C. Basquin, A. Reyna-Neyra, L. M. Amzel, and N. Carrasco The Na+/I symporter (NIS) mediates electroneutral active transport of the environmental pollutant perchlorate PNAS, December 18, 2007; 104(51): 20250 - 20255. [Abstract] [Full Text] [PDF]

				S. Amachi, K. Kimura, Y. Muramatsu, H. Shinoyama, and T. Fujii Hydrogen Peroxide-Dependent Uptake of Iodine by Marine Flavobacteriaceae Bacterium Strain C-21 Appl. Envir. Microbiol., December 1, 2007; 73(23): 7536 - 7541. [Abstract] [Full Text] [PDF]

				A. Goel, S. K. Carlson, K. L. Classic, S. Greiner, S. Naik, A. T. Power, J. C. Bell, and S. J. Russell Radioiodide imaging and radiovirotherapy of multiple myeloma using VSV({Delta}51)-NIS, an attenuated vesicular stomatitis virus encoding the sodium iodide symporter gene Blood, October 1, 2007; 110(7): 2342 - 2350. [Abstract] [Full Text] [PDF]

				L. V. Virkki, J. Biber, H. Murer, and I. C. Forster Phosphate transporters: a tale of two solute carrier families Am J Physiol Renal Physiol, September 1, 2007; 293(3): F643 - F654. [Abstract] [Full Text] [PDF]

				A. De la Vieja, M. D. Reed, C. S. Ginter, and N. Carrasco Amino Acid Residues in Transmembrane Segment IX of the Na+/I Symporter Play a Role in Its Na+ Dependence and Are Critical for Transport Activity J. Biol. Chem., August 31, 2007; 282(35): 25290 - 25298. [Abstract] [Full Text] [PDF]

				S. Ravera, L. V. Virkki, H. Murer, and I. C. Forster Deciphering PiT transport kinetics and substrate specificity using electrophysiology and flux measurements Am J Physiol Cell Physiol, August 1, 2007; 293(2): C606 - C620. [Abstract] [Full Text] [PDF]

				D. D Vadysirisack, A. Venkateswaran, Z. Zhang, and S. M Jhiang MEK signaling modulates sodium iodide symporter at multiple levels and in a paradoxical manner Endocr. Relat. Cancer, June 1, 2007; 14(2): 421 - 432. [Abstract] [Full Text] [PDF]

				K. J. Rhoden, S. Cianchetta, V. Stivani, C. Portulano, L. J. V. Galietta, and G. Romeo Cell-based imaging of sodium iodide symporter activity with the yellow fluorescent protein variant YFP-H148Q/I152L Am J Physiol Cell Physiol, February 1, 2007; 292(2): C814 - C823. [Abstract] [Full Text] [PDF]

				O Arroyo-Helguera, B Anguiano, G Delgado, and C Aceves Uptake and antiproliferative effect of molecular iodine in the MCF-7 breast cancer cell line Endocr. Relat. Cancer, December 1, 2006; 13(4): 1147 - 1158. [Abstract] [Full Text] [PDF]

				K.-H. Lee, J.-S. Bae, S.-C. Lee, J.-Y. Paik, T. Matsui, K.-H. Jung, B.-H. Ko, and B.-T. Kim Evidence that Myocardial Na/I Symporter Gene Imaging Does Not Perturb Cardiac Function J. Nucl. Med., November 1, 2006; 47(11): 1851 - 1857. [Abstract] [Full Text] [PDF]

				H. Iwamoto, R. D. Blakely, and L. J. De Felice Na+, Cl-, and pH Dependence of the Human Choline Transporter (hCHT) in Xenopus Oocytes: The Proton Inactivation Hypothesis of hCHT in Synaptic Vesicles J. Neurosci., September 27, 2006; 26(39): 9851 - 9859. [Abstract] [Full Text] [PDF]

				M. Quick, H. Yano, N. R. Goldberg, L. Duan, T. Beuming, L. Shi, H. Weinstein, and J. A. Javitch State-dependent Conformations of the Translocation Pathway in the Tyrosine Transporter Tyt1, a Novel Neurotransmitter:Sodium Symporter from Fusobacterium nucleatum J. Biol. Chem., September 8, 2006; 281(36): 26444 - 26454. [Abstract] [Full Text] [PDF]

				B. De Groef, B. R Decallonne, S. Van der Geyten, V. M Darras, and R. Bouillon Perchlorate versus other environmental sodium/iodide symporter inhibitors: potential thyroid-related health effects. Eur. J. Endocrinol., July 1, 2006; 155(1): 17 - 25. [Abstract] [Full Text] [PDF]

				M. Sala-Rabanal, D. D. F. Loo, B. A. Hirayama, E. Turk, and E. M. Wright Molecular interactions between dipeptides, drugs and the human intestinal H+-oligopeptide cotransporter hPEPT1 J. Physiol., July 1, 2006; 574(1): 149 - 166. [Abstract] [Full Text] [PDF]

				V. Paroder, S. R. Spencer, M. Paroder, D. Arango, S. Schwartz Jr., J. M. Mariadason, L. H. Augenlicht, S. Eskandari, and N. Carrasco Na+/monocarboxylate transport (SMCT) protein expression correlates with survival in colon cancer: Molecular characterization of SMCT PNAS, May 9, 2006; 103(19): 7270 - 7275. [Abstract] [Full Text] [PDF]

				M S Allagui, N Hfaiedh, C Vincent, F Guermazi, J-C Murat, F Croute, and A E. Feki Changes in growth rate and thyroid- and sex-hormones blood levels in rats under sub-chronic lithium treatment Human and Experimental Toxicology, May 1, 2006; 25(5): 243 - 250. [Abstract] [PDF]

				O. Dohan, A. De la Vieja, and N. Carrasco Hydrocortisone and Purinergic Signaling Stimulate Sodium/Iodide Symporter (NIS)-Mediated Iodide Transport in Breast Cancer Cells Mol. Endocrinol., May 1, 2006; 20(5): 1121 - 1137. [Abstract] [Full Text] [PDF]

				M. Josefsson, L. Evilevitch, B. Westrom, T. Grunditz, and E. Ekblad Sodium-iodide symporter mediates iodide secretion in rat gastric mucosa in vitro. Experimental Biology and Medicine, March 1, 2006; 231(3): 277 - 281. [Abstract] [Full Text] [PDF]

				T. Zeuthen*, B. Belhage, and E. Zeuthen Water transport by Na+-coupled cotransporters of glucose (SGLT1) and of iodide (NIS). The dependence of substrate size studied at high resolution J. Physiol., February 1, 2006; 570(3): 485 - 499. [Abstract] [Full Text] [PDF]

				D. D. Vadysirisack, D. H. Shen, and S. M. Jhiang Correlation of Na+/I- Symporter Expression and Activity: Implications of Na+/I- Symporter as an Imaging Reporter Gene J. Nucl. Med., January 1, 2006; 47(1): 182 - 190. [Abstract] [Full Text] [PDF]

				A. De la Vieja, C. S. Ginter, and N. Carrasco Molecular Analysis of a Congenital Iodide Transport Defect: G543E Impairs Maturation and Trafficking of the Na+/I- Symporter Mol. Endocrinol., November 1, 2005; 19(11): 2847 - 2858. [Abstract] [Full Text] [PDF]

				Z. Zhang, Y.-Y. Liu, and S. M. Jhiang Cell Surface Targeting Accounts for the Difference in Iodide Uptake Activity between Human Na+/I- Symporter and Rat Na+/I- Symporter J. Clin. Endocrinol. Metab., November 1, 2005; 90(11): 6131 - 6140. [Abstract] [Full Text] [PDF]

				N. Oshiro and A. M. Pajor Functional characterization of high-affinity Na+/dicarboxylate cotransporter found in Xenopus laevis kidney and heart Am J Physiol Cell Physiol, November 1, 2005; 289(5): C1159 - C1168. [Abstract] [Full Text] [PDF]

				M. Irie, T. Terada, T. Katsura, S. Matsuoka, and K.-i. Inui Computational modelling of H+-coupled peptide transport via human PEPT1 J. Physiol., June 1, 2005; 565(2): 429 - 439. [Abstract] [Full Text] [PDF]

				L. V. Virkki, I. C. Forster, J. Biber, and H. Murer Substrate interactions in the human type IIa sodium-phosphate cotransporter (NaPi-IIa) Am J Physiol Renal Physiol, May 1, 2005; 288(5): F969 - F981. [Abstract] [Full Text] [PDF]

				S. Amachi, Y. Mishima, H. Shinoyama, Y. Muramatsu, and T. Fujii Active Transport and Accumulation of Iodide by Newly Isolated Marine Bacteria Appl. Envir. Microbiol., February 1, 2005; 71(2): 741 - 745. [Abstract] [Full Text] [PDF]

				A. C F Ferreira, L. P Lima, R. L Araujo, G. Muller, R. P Rocha, D. Rosenthal, and D. P Carvalho Rapid regulation of thyroid sodium-iodide symporter activity by thyrotrophin and iodine J. Endocrinol., January 1, 2005; 184(1): 69 - 76. [Abstract] [Full Text] [PDF]

				E. A. Merrill, R. A. Clewell, P. J. Robinson, A. M. Jarabek, J. M. Gearhart, T. R. Sterner, and J. W. Fisher PBPK Model for Radioactive Iodide and Perchlorate Kinetics and Perchlorate-Induced Inhibition of Iodide Uptake in Humans Toxicol. Sci., January 1, 2005; 83(1): 25 - 43. [Abstract] [Full Text] [PDF]

				K. I. Kim, J.-K. Chung, J. H. Kang, Y. J. Lee, J. H. Shin, H. J. Oh, J. M. Jeong, D. S. Lee, and M. C. Lee Visualization of Endogenous p53-Mediated Transcription In vivo Using Sodium Iodide Symporter Clin. Cancer Res., January 1, 2005; 11(1): 123 - 128. [Abstract] [Full Text] [PDF]

				M. Miyagawa, M. Beyer, B. Wagner, M. Anton, C. Spitzweg, B. Gansbacher, M. Schwaiger, and F. M. Bengel Cardiac reporter gene imaging using the human sodium/iodide symporter gene Cardiovasc Res, January 1, 2005; 65(1): 195 - 202. [Abstract] [Full Text] [PDF]

				M. A Fragoso, V. Fernandez, R. Forteza, S. H Randell, M. Salathe, and G. E Conner Transcellular thiocyanate transport by human airway epithelia J. Physiol., November 15, 2004; 561(1): 183 - 194. [Abstract] [Full Text] [PDF]

				K. M. Smith, A. M. L. Ng, S. Y. M. Yao, K. A. Labedz, E. E. Knaus, L. I. Wiebe, C. E. Cass, S. A. Baldwin, X.-Z. Chen, E. Karpinski, et al. Electrophysiological characterization of a recombinant human Na+-coupled nucleoside transporter (hCNT1) produced in Xenopus oocytes J. Physiol., August 1, 2004; 558(3): 807 - 823. [Abstract] [Full Text] [PDF]

				M. J. Coady, M.-H. Chang, F. M. Charron, C. Plata, B. Wallendorff, J. F. Sah, S. D. Markowitz, M. F. Romero, and J.-Y. Lapointe The human tumour suppressor gene SLC5A8 expresses a Na+-monocarboxylate cotransporter J. Physiol., June 15, 2004; 557(3): 719 - 731. [Abstract] [Full Text] [PDF]

				L. S. Zuckier, O. Dohan, Y. Li, C. J. Chang, N. Carrasco, and E. Dadachova Kinetics of Perrhenate Uptake and Comparative Biodistribution of Perrhenate, Pertechnetate, and Iodide by NaI Symporter-Expressing Tissues In Vivo J. Nucl. Med., March 1, 2004; 45(3): 500 - 507. [Abstract] [Full Text]

				A. De la Vieja, C. S. Ginter, and N. Carrasco The Q267E mutation in the sodium/iodide symporter (NIS) causes congenital iodide transport defect (ITD) by decreasing the NIS turnover number J. Cell Sci., February 15, 2004; 117(5): 677 - 687. [Abstract] [Full Text] [PDF]

				R. A. Clewell, E. A. Merrill, L. Narayanan, J. M. Gearhart, and P. J. Robinson Evidence for Competitive Inhibition of Iodide Uptake by Perchlorate and Translocation of Perchlorate into the Thyroid International Journal of Toxicology, January 1, 2004; 23(1): 17 - 23. [Abstract] [Full Text] [PDF]

				T. Kogai, Y. Kanamoto, L. H. Che, K. Taki, F. Moatamed, J. J. Schultz, and G. A. Brent Systemic Retinoic Acid Treatment Induces Sodium/Iodide Symporter Expression and Radioiodide Uptake in Mouse Breast Cancer Models Cancer Res., January 1, 2004; 64(1): 415 - 422. [Abstract] [Full Text] [PDF]

				A.-C. Gerard, C. Daumerie, C. Mestdagh, S. Gohy, C. de Burbure, S. Costagliola, F. Miot, M.-C. Nollevaux, J.-F. Denef, J. Rahier, et al. Correlation between the Loss of Thyroglobulin Iodination and the Expression of Thyroid-Specific Proteins Involved in Iodine Metabolism in Thyroid Carcinomas J. Clin. Endocrinol. Metab., October 1, 2003; 88(10): 4977 - 4983. [Abstract] [Full Text] [PDF]

				R. D. Whitlow, A. Sacher, D. D. F. Loo, N. Nelson, and S. Eskandari The Anticonvulsant Valproate Increases the Turnover Rate of gamma -Aminobutyric Acid Transporters J. Biol. Chem., May 9, 2003; 278(20): 17716 - 17726. [Abstract] [Full Text] [PDF]

				O. Dohan, A. De la Vieja, V. Paroder, C. Riedel, M. Artani, M. Reed, C. S. Ginter, and N. Carrasco The Sodium/Iodide Symporter (NIS): Characterization, Regulation, and Medical Significance Endocr. Rev., February 1, 2003; 24(1): 48 - 77. [Abstract] [Full Text] [PDF]

				J. Van Sande, C. Massart, R. Beauwens, A. Schoutens, S. Costagliola, J. E. Dumont, and J. Wolff Anion Selectivity by the Sodium Iodide Symporter Endocrinology, January 1, 2003; 144(1): 247 - 252. [Abstract] [Full Text] [PDF]

				K. Kohler, I. C. Forster, G. Stange, J. Biber, and H. Murer Transport Function of the Renal Type IIa Na+/Pi Cotransporter Is Codetermined by Residues in Two Opposing Linker Regions J. Gen. Physiol., October 29, 2002; 120(5): 693 - 705. [Abstract] [Full Text] [PDF]

				J.-K. Chung Sodium Iodide Symporter: Its Role in Nuclear Medicine J. Nucl. Med., September 1, 2002; 43(9): 1188 - 1200. [Abstract] [Full Text] [PDF]

				O. Dohan, M. V. Gavrielides, C. Ginter, L. M. Amzel, and N. Carrasco Na+/I- Symporter Activity Requires a Small and Uncharged Amino Acid Residue at Position 395 Mol. Endocrinol., August 1, 2002; 16(8): 1893 - 1902. [Abstract] [Full Text] [PDF]

				A.-C. Gerard, M.-C. Many, C. Daumerie, S. Costagliola, F. Miot, J. J. M. DeVijlder, I. M. Colin, and J.-F. Denef Structural Changes in the Angiofollicular Units between Active and Hypofunctioning Follicles Align with Differences in the Epithelial Expression of Newly Discovered Proteins Involved in Iodine Transport and Organification J. Clin. Endocrinol. Metab., March 1, 2002; 87(3): 1291 - 1299. [Abstract] [Full Text] [PDF]

				D. Cauvi, M.-C. Nlend, N. Venot, and O. Chabaud Sulfate transport in porcine thyroid cells. Effects of thyrotropin and iodide Am J Physiol Endocrinol Metab, September 1, 2001; 281(3): E440 - E448. [Abstract] [Full Text] [PDF]

				E. M. Wright Renal Na+-glucose cotransporters Am J Physiol Renal Physiol, January 1, 2001; 280(1): F10 - F18. [Abstract] [Full Text] [PDF]

				Y. Nakamoto, T. Saga, T. Misaki, H. Kobayashi, N. Sato, T. Ishimori, S. Kosugi, H. Sakahara, and J. Konishi Establishment and Characterization of a Breast Cancer Cell Line Expressing Na+/I- Symporters for Radioiodide Concentrator Gene Therapy J. Nucl. Med., November 1, 2000; 41(11): 1898 - 1904. [Abstract] [Full Text] [PDF]

				D. W Leung, D. D F Loo, B. A Hirayama, T. Zeuthen, and E. M Wright Urea transport by cotransporters J. Physiol., October 15, 2000; 528(2): 251 - 257. [Abstract] [Full Text] [PDF]

				H. Murer, N. Hernando, I. Forster, and J. Biber Proximal Tubular Phosphate Reabsorption: Molecular Mechanisms Physiol Rev, October 1, 2000; 80(4): 1373 - 1409. [Abstract] [Full Text] [PDF]

				M. H. Saier Jr Families of transmembrane transporters selective for amino acids and their derivatives Microbiology, August 1, 2000; 146(8): 1775 - 1795. [Full Text]

				S. Eskandari, M. Kreman, M. P. Kavanaugh, E. M. Wright, and G. A. Zampighi Pentameric assembly of a neuronal glutamate transporter PNAS, July 18, 2000; 97(15): 8641 - 8646. [Abstract] [Full Text] [PDF]

				T. Kogai, J. J. Schultz, L. S. Johnson, M. Huang, and G. A. Brent Retinoic acid induces sodium/iodide symporter gene expression and radioiodide uptake in the MCF-7 breast cancer cell line PNAS, July 5, 2000; (2000) 140217197. [Abstract] [Full Text]

				A. Boland, M. Ricard, P. Opolon, J.-M. Bidart, P. Yeh, S. Filetti, M. Schlumberger, and M. Perricaudet Adenovirus-mediated Transfer of the Thyroid Sodium/Iodide Symporter Gene into Tumors for a Targeted Radiotherapy Cancer Res., July 1, 2000; 60(13): 3484 - 3492. [Abstract] [Full Text]

				A. De la Vieja, O. Dohan, O. Levy, and N. Carrasco Molecular Analysis of the Sodium/Iodide Symporter: Impact on Thyroid and Extrathyroid Pathophysiology Physiol Rev, July 1, 2000; 80(3): 1083 - 1105. [Abstract] [Full Text] [PDF]

				X. Yao and A. M. Pajor The transport properties of the human renal Na+- dicarboxylate cotransporter under voltage-clamp conditions Am J Physiol Renal Physiol, July 1, 2000; 279(1): F54 - F64. [Abstract] [Full Text] [PDF]

				S. Eskandari, P. M. Snyder, M. Kreman, G. A. Zampighi, M. J. Welsh, and E. M. Wright Number of Subunits Comprising the Epithelial Sodium Channel J. Biol. Chem., September 17, 1999; 274(38): 27281 - 27286. [Abstract] [Full Text] [PDF]

				I. C. Forster, D. D. F. Loo, and S. Eskandari Stoichiometry and Na+ binding cooperativity of rat and flounder renal type II Na+-Pi cotransporters Am J Physiol Renal Physiol, April 1, 1999; 276(4): F644 - F649. [Abstract] [Full Text] [PDF]

				X.-Z. Chen, T. Zhu, D. E. Smith, and M. A. Hediger Stoichiometry and Kinetics of the High-affinity H+-coupled Peptide Transporter PepT2 J. Biol. Chem., January 29, 1999; 274(5): 2773 - 2779. [Abstract] [Full Text] [PDF]

				B. Caillou, F. Troalen, E. Baudin, M. Talbot, S. Filetti, M. Schlumberger, and J.-M. Bidart Na+/I- Symporter Distribution in Human Thyroid Tissues: An Immunohistochemical Study J. Clin. Endocrinol. Metab., November 1, 1998; 83(11): 4102 - 4106. [Abstract] [Full Text]

				S. Eskandari, E. M. Wright, M. Kreman, D. M. Starace, and G. A. Zampighi Structural analysis of cloned plasma membrane proteins by freeze-fracture electron microscopy PNAS, September 15, 1998; 95(19): 11235 - 11240. [Abstract] [Full Text] [PDF]

				O. Levy, A. De la Vieja, C. S. Ginter, C. Riedel, G. Dai, and N. Carrasco N-linked Glycosylation of the Thyroid Na+/I- Symporter (NIS). IMPLICATIONS FOR ITS SECONDARY STRUCTURE MODEL J. Biol. Chem., August 28, 1998; 273(35): 22657 - 22663. [Abstract] [Full Text] [PDF]

				A. M. Pajor, B. A. Hirayama, and D. D. F. Loo Sodium and Lithium Interactions with the Na+/Dicarboxylate Cotransporter J. Biol. Chem., July 24, 1998; 273(30): 18923 - 18929. [Abstract] [Full Text] [PDF]

				X. De Deken, D. Wang, M.-C. Many, S. Costagliola, F. Libert, G. Vassart, J. E. Dumont, and F. Miot Cloning of Two Human Thyroid cDNAs Encoding New Members of the NADPH Oxidase Family J. Biol. Chem., July 21, 2000; 275(30): 23227 - 23233. [Abstract] [Full Text] [PDF]

				Z. Xie, E. Turk, and E. M. Wright Characterization of the Vibrio parahaemolyticus Na+/Glucose Cotransporter. A BACTERIAL MEMBER OF THE SODIUM/GLUCOSE TRANSPORTER (SGLT) FAMILY J. Biol. Chem., August 18, 2000; 275(34): 25959 - 25964. [Abstract] [Full Text] [PDF]

				D. D. F. Loo, S. Eskandari, K. J. Boorer, H. K. Sarkar, and E. M. Wright Role of Cl- in Electrogenic Na+-coupled Cotransporters GAT1 and SGLT1 J. Biol. Chem., November 22, 2000; 275(48): 37414 - 37422. [Abstract] [Full Text] [PDF]

				C. Riedel, O. Levy, and N. Carrasco Post-transcriptional Regulation of the Sodium/Iodide Symporter by Thyrotropin J. Biol. Chem., June 8, 2001; 276(24): 21458 - 21463. [Abstract] [Full Text] [PDF]

				M. Quick and B. R. Stevens Amino Acid Transporter CAATCH1 Is Also an Amino Acid-gated Cation Channel J. Biol. Chem., August 31, 2001; 276(36): 33413 - 33418. [Abstract] [Full Text] [PDF]

				D. H. Feldman, W. R. Harvey, and B. R. Stevens A Novel Electrogenic Amino Acid Transporter Is Activated by K+ or Na+, Is Alkaline pH-dependent, and Is Cl--independent J. Biol. Chem., August 4, 2000; 275(32): 24518 - 24526. [Abstract] [Full Text] [PDF]

				T. Kogai, J. J. Schultz, L. S. Johnson, M. Huang, and G. A. Brent Retinoic acid induces sodium/iodide symporter gene expression and radioiodide uptake in the MCF-7 breast cancer cell line PNAS, July 18, 2000; 97(15): 8519 - 8524. [Abstract] [Full Text] [PDF]

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