| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
J Biol Chem, Vol. 273, Issue 38, 24737-24743, September 18, 1998
From the Renal Division, Department of Medicine, Brigham & Women's
Hospital and Harvard Medical School, Boston, Massachusetts 02115, the
In all living cells, coordination of solute and
water movement across cell membranes is of critical importance for
osmotic balance. The current concept is that these processes are of
distinct biophysical nature. Here we report the expression cloning of a liver cDNA encoding a unique promiscuous solute channel (AQP9) that
confers high permeability for both solutes and water. AQP9 mediates
passage of a wide variety of non-charged solutes including carbamides,
polyols, purines, and pyrimidines in a phloretin- and mercury-sensitive
manner, whereas amino acids, cyclic sugars, Na+,
K+, Cl Transport of solutes such as ions, nutrients, neurotransmitters,
and metabolic waste products across cell membranes is of fundamental
importance to all mammalian cells. Despite the identification of many
selective solute transporters and water channels (1-4), it has
remained unclear how transport of large amounts of solutes is
coordinated with water movement in metabolically highly active cells
such as hepatocytes, spermatocytes, neurons, and glia. The liver is a
major site of production and elimination of metabolites such as urea,
nucleotides, and ketone bodies, and substantial amounts of these
solutes must rapidly cross the hepatocyte plasma membrane with minimal
osmotic perturbation (5). In testis, a solute transport mechanism is
presumably required to supply nutrients to rapidly growing
spermatocytes and to provide an exit pathway for metabolites. In brain,
regulation of solute transport is critical because osmolality changes
in extracellular fluids can affect neuronal cell function (6).
Among metabolically active tissues, liver was selected as a target for
expression cloning of a new solute-transporting protein because a
phloretin-sensitive urea exit mechanism had been described (7-9).
Expression Cloning--
Total RNA was extracted from rats fed a
high protein diet (50%, w/w) for 2 weeks. Poly(A)+ RNA
purified by oligo(dT) chromatography was size-fractionated by
preparative agarose gel electrophoresis (30). Specific fractions were
screened for 1 mM [14C]urea uptake activity
in RNA-injected Xenopus oocytes (4, 30). A directional
cDNA library was constructed from the positive fraction by using
the SuperScript Plasmid System (Life Technologies, Inc.), and cDNA
clones were screened for urea uptake (4).
Northern Analysis and in Situ
Hybridization--
Poly(A)+ RNA (3 µg) from rat tissues
was electrophoresed in a formaldehyde-agarose gel and transferred to a
nylon membrane. The filter was probed with 32P-labeled
full-length AQP91 cDNA,
hybridized at 42 °C, and washed with 0.1% SDS, 0.1× SSC, at
65 °C. Autoradiography was performed at Oocyte Expression and Radiotracer Uptake Assay--
AQP9-cRNA
was synthesized from pSPORT1 after linearization with NotI,
using T7 RNA polymerase. Human AQP1-cDNA (a gift of Dr. Peter Agre)
and rat AQP3-cDNA (a gift of Dr. Gustavo Frindt) were prepared as
described previously (11, 12). AQP1-cRNA (10 ng), AQP3-cRNA, and
AQP9-cRNA (25 ng) were injected into collagenase-treated, manually
defolliculated oocytes maintained at 18 °C for 2-3 days prior to
assays. Radiotracer studies were performed as described (10). Briefly,
oocytes were incubated for 90 s with Barth's solution (88 mM NaCl, 1 mM KCl, 0.33 mM
Ca(NO3)2, 0.41 mM
CaCl2, 0.82 mM MgSO4, 2.4 mM NaHCO3, 10 mM HEPES, pH 7.4)
including 1 mM unlabeled compound and 1-2 µCi/ml
radiolabeled compound. Uptake was terminated by adding ice-cold
Barth's solution with 1 mM unlabeled compound, and
oocytes were solubilized in 200 µl of 10% SDS. Ps (where Ps indicates diffusive solute
permeability coefficient (cm/s)) was determined from the following
relation: Ps = N/(A × Volumetric Assays--
Water permeability was determined by
volumetric swelling induced by hypotonic perturbation of oocytes (12).
The oocytes were transferred from 200 to 70 mosm of diluted Barth's
solution at 22 °C; oocyte swelling was monitored by video
microscopy, and the coefficient of osmotic water permeability
(Pf) was determined. The Arrhenius activation
energy was calculated from Pf at 4, 22, and
30 °C. Iso-osmotic swelling assays were performed as described (11).
Briefly, the swelling rate of the oocytes was measured by a video
microscope every 10 s for 2 min, after transferring the oocytes
from standard Barth's solution to modified Barth's solution in which
88 mM NaCl was replaced by solutes (adjusted to final
osmolality of 200 ± 20 mosm) or water. Osmolality was measured by
freezing point depression.
Electrophysiological Studies--
A two-microelectrode voltage
clamp (Dagan Clampator-1B) was used to measure currents in
water-injected oocytes and oocytes expressing AQP1 or AQP9.
Microelectrodes (1-5 M Expression Cloning of AQP9 cDNA--
We first determined 1 mM [14C]urea uptake in Xenopus
oocytes injected with rat liver mRNA. RNA-injected oocytes
exhibited a 2-fold increase in urea uptake compared with water-injected
controls (Fig. 1A). When rats
were fed a high protein diet, liver mRNA injection induced an
8-fold increase in urea uptake. Liver mRNA from rats fed a high
protein diet was fractionated by preparative agarose gel
electrophoresis (4), and fractions were analyzed by oocyte expression.
A fraction of size 1.5-2.0 kb maximally stimulated urea uptake
(
Molecular Characterization of a Broad Selectivity Neutral
Solute Channel*
,
,,, and Department of Physiology, The Johns Hopkins University School of
Medicine, Baltimore, Maryland 21205, and the ** Renal Unit,
Massachusetts General Hospital and Harvard Medical School,
Boston, Massachusetts 02129
ABSTRACT
Top
Abstract
Introduction
Materials & Methods
Results & Discussion
References
, and deprotonated
monocarboxylates are excluded. The properties of AQP9 define a new
evolutionary branch of the major intrinsic protein family of aquaporin
proteins and describe a previously unknown mechanism by which a large
variety of solutes and water can pass through a single pore, enabling
rapid cellular uptake or exit of metabolites with minimal osmotic
perturbation.
INTRODUCTION
Top
Abstract
Introduction
Materials & Methods
Results & Discussion
References
MATERIALS AND METHODS
Top
Abstract
Introduction
Materials & Methods
Results & Discussion
References
80 °C for 5 days. Digoxigenin-labeled sense and antisense probes were synthesized as
described (10) and hybridized on 12-µm cryosections of fresh-frozen rat liver and testis. The hybridized probes were visualized using digoxigenin Fab fragment (Boehringer Mannheim) and bromochloroindolyl phosphate/nitro blue tetrazolium substrate.
c), where N is radiotracer uptake (pmol/s);
A is the membrane area (0.045 cm2), and
c is the concentration difference of the solute (in
pmol/cm3). The Arrhenius activation energy was calculated
from Ps values at 4, 22, and 30 °C.
) were filled with 3 M KCl.
Oocytes were superfused at 23 ± 1 °C in Barth's medium and
clamped at a holding potential of 50 mV. Step changes in membrane
potential (between +50 and 150 mV, in 20-mV increments) were applied
for a duration of 100 ms. Current was filtered at 500 Hz, digitized at
5 kHz, and acquired using the Digidata1200 interface and pCLAMP6
software (Axon Instruments). The steady-state current-voltage
relationships were determined with the help of software written by
Donald D. F. Loo, UCLA School of Medicine. Functional expression
of AQP9 or AQP1 in individual oocytes used for voltage-clamp
experiments was subsequently confirmed by radiotracer uptakes or
osmotic swelling (lysis) measurements.
RESULTS AND DISCUSSION
Top
Abstract
Introduction
Materials & Methods
Results & Discussion
References
12-fold above background, data not shown). This fraction was used
to construct a cDNA library from which we isolated a 1.5-kb
cDNA that encodes a 295-amino acid residue hydrophobic protein,
AQP9. AQP9 has low-to-moderate homology with the mammalian aquaporins
AQP3 (48% identity) (11, 13, 14), AQP7 (46% identity) (15), AQP1
(30% identity) (1-3), and with the bacterial glycerol facilitator
GlpF (37% identity) (16) (Fig. 1, B and C). A
homologue of AQP9 was recently reported from human leucocytes (17), but
its unique properties have not yet been investigated. There is no
significant homology with members of the urea transporter family.
Kyte-Doolittle hydropathy analysis predicted six transmembrane domains
separated by five connecting loops (Fig. 1D). AQP9 has two
Asn-Pro-Ala (NPA) consensus motifs, characteristic of members of the
major intrinsic protein (MIP) family (1-3) (Fig. 1B).
View larger version (41K):
[in a new window]
Fig. 1.
Expression cloning and deduced amino acid
sequence of AQP9. A, uptake of 1 mM
[14C]urea in Xenopus oocytes injected with 50 ng of poly(A)+ RNA from rats fed normal and high protein
(50% w/w) diets. B, amino acid sequence alignment of AQP9,
rat AQP1 (GenBankTM P29975), rat AQP3
(GenBankTM L35108), rat AQP7 (GenBankTM
AB000507), and Escherichia coli GlpF (GenBankTM
M55990) was performed using the PILEUP program (Genetics Computer
Group). Putative membrane-spanning regions are underlined
and numbered 1-6. Conserved residues are indicated by
shading. Asn-Pro-Ala (NPA) consensus motifs are highlighted
by boxes. The potential sites for N-linked
glycosylation (Asn-142) (double line), protein kinase C
phosphorylation site (Ser-222), and casein kinase II phosphorylation
site (Ser-271) (asterisks) are depicted. No consensus motifs
of protein kinase A phosphorylation were found. C,
phylogenic analysis of AQP9. Deduced amino acid sequences were analyzed
using PILEUP. The percent amino acid identity between AQP9 and others
is indicated. D, structural model of AQP9. Topology was
determined according to the Kyte-Doolittle algorithm. The numbering of
putative membrane-spanning regions corresponds to those of
B.
Tissue Localization of AQP9-- High stringency Northern analysis revealed a strong 1.5-kb transcript in liver (Fig. 2A). Signals of 2.2 kb were detected in testis and brain, suggesting alternative splicing or use of different polyadenylation sites. No hybridization signals were detected in kidney, colon, heart, and skeletal muscle. Nonradioactive in situ hybridization in rat liver showed that AQP9 is expressed evenly among hepatocytes (Fig. 2B). In testis, AQP9 mRNA was detected in the inner surface of seminiferous tubules and in the interstitial Leydig cells. In seminiferous tubules, signals were obtained in spermatocytes at early developmental stages but not at later stages and not in Sertoli cells. AQP9 mRNA was detected in astrocytes throughout the brain (data not shown).
|
Functional Expression in Xenopus Oocytes--
When expressed in
cRNA-injected oocytes, AQP9 increased the urea permeability coefficient
(Ps) from 1.5 × 106 ± 0.2 × 106 cm/s (water-injected) to 23.5 × 106 ± 2.0 × 106 cm/s (Fig.
3A). The increase in
Ps was similar to that observed in oocytes
expressing the urea transporters UT2 and UT3 (Ps
= 25-45 × 106 cm/s) (cf.
Refs. 4, 10, and 18). The activation energy estimated from
Arrhenius plots was 7.8 ± 1.5 kcal/mol, consistent with movement through a pore. We then determined the selectivity of the AQP9 pore
(Fig. 3A) and obtained Ps values for
polyols (glycerol, mannitol, and sorbitol), purines (adenine),
pyrimidines (uracil and the chemotherapeutic agent 5-fluorouracil), and
urea analogues (thiourea) ranging from 15 to 25 × 106 cm/s, suggesting a promiscuous permselectivity
profile for AQP9. Radiotracer uptake studies revealed that AQP9 was
impermeable to cyclic sugars (D-glucose,
D-mannose, and myo-inositol), the nucleoside
uridine, and amino acids (glutamine and glycine) (data not shown).
|
-hydroxybutyrate,
each of physiological importance in hepatocytes. Their
Ps values were significantly increased at
physiological pH, but an additional 4-fold increase was observed at pH
5.5 (Fig. 3B), whereas mannitol uptake was independent of
pH. In voltage-clamped oocytes expressing AQP9, monocarboxylates at
concentrations up to 10 mM evoked no significant currents
(less than 5 nA), regardless of pHo. Together with pH
dependence of radiotracer uptakes, these results indicate that
monocarboxylates permeate AQP9 only in their protonated form. The low
permeabilities of the purine analogues xanthine and uric acid at pH 7.4 suggest that, likewise, these compounds permeate AQP9 in their
protonated form (Fig. 3A).
We measured radiotracer uptake in oocytes expressing the aquaporins
AQP1 and AQP3 to compare their solute permeabilities with those of AQP9
(Fig. 3C). AQP1 did not mediate significant uptake of any
solute tested, indicating that AQP1 is a selective water channel
(1-3). AQP3 facilitated glycerol uptake at levels similar to that for
AQP9, but a weak urea permeability was detected in AQP3 (25% of the
Ps value for AQP9). In addition, AQP3 was
impermeable to the urea analogue thiourea, to polyols larger than
glycerol, and to purines and pyrimidines. Our results suggest that the
pore selectivity in the aquaporins decreases in the order AQP1 > AQP3 > AQP9. The osmotic permeability coefficient
Pf was increased 30-fold (to 0.014 ± 0.0013 cm/s) in oocytes expressing AQP9 (cf. 0.0005 ± 0.00002 cm/s in water-injected oocytes) (Fig. 3D). AQP9 showed a Pf similar to that for AQP1 (0.016 ± 0.0014 cm/s), but AQP3 exhibited a lower Pf
(0.0073 ± 0.0008 cm/s). The Arrhenius activation energy for
AQP9-mediated Pf was 3.6 ± 1.3 kcal/mol, again consistent with movement through a pore (1-3).
Notably, unlike other known aquaporins, water permeability was
sensitive to 0.1 mM phloretin (86% inhibition). In AQP9,
Pf was reduced 61% in the presence of 0.3 mM HgCl2. A cysteine residue thought to be
involved in mercurial binding lies 3 amino acid residues
N-terminal to the second NPA box (1-3). Thus, AQP9
possesses general features of water channels in addition to the
distinctive phloretin-inhibitable permeability for a large variety of
non-charged solutes.
Ion Conductance of AQP9--
It has been generally considered that
none of the aquaporins mediates any type of ion conductance under
normal conditions (1-3). A recent report (19) suggested that forskolin
induced a nonspecific cation conductance via AQP1, despite the absence of a typical consensus protein kinase A phosphorylation site. This
phenomenon has been disputed by others (20) applying the same
protocols. By using voltage-clamped oocytes expressing either AQP1 or
AQP9, we determined the macroscopic conductance from the slope of the
linear current-voltage relationship (between +50 mV and 150 mV)
before and after superfusion with 10 µM forskolin in
Barth's solution for 15 min (Fig. 3E). Only low ionic
conductance was observed in the presence and absence of forskolin, in
oocytes expressing AQP1 or AQP9, and in water-injected oocytes. The
reversal potential was unchanged in all groups following forskolin
treatment. Forskolin administered by direct microinjection into the
oocytes was also ineffective (not shown). Therefore, neither AQP1 nor AQP9 mediates any ionic conductance under basal or forskolin-treated conditions.
Inhibition Profiles of AQP9--
A fundamental question is whether
or not solutes and water share a single pore in AQP9. To address this
issue, we first examined the inhibition profiles of solute
permeabilities by phloretin and mercurial compounds. Phloretin (0.1 mM) and HgCl2 (0.3 mM) effectively
inhibited the water permeability as well as the permeabilities for
mannitol, uracil, adenine, and -hydroxybutyrate (75-90%) (Fig.
3F). Glycerol and urea permeabilities were inhibited
35-45% by 0.1 mM phloretin. Glycerol permeability was
inhibited 50% by 0.3 mM HgCl2, but urea
permeability was not significantly affected by HgCl2. In
oocytes expressing AQP3, water and urea permeabilities were partially
inhibited by 0.1 mM phloretin and 0.3 mM
HgCl2 (15-20%), whereas the glycerol permeability was
unchanged. The similar inhibition profiles of solute and water
permeabilites in AQP9 indicate that solutes and water share a common
transmembrane pathway.
Determination of Reflection Coefficients-- This common pathway was further investigated by volumetric assays under iso-osmotic conditions as well as by mathematical simulation of water and solute flows. Oocytes expressing AQP9 were transferred from standard Barth's solution into Barth's solution containing test solute (176 mosm). In AQP9 expressing oocytes, rapid swelling was observed for mannitol and glycerol (Fig. 4A), whereas in AQP3 expressing oocytes, rapid swelling was observed only for glycerol (Fig. 4B). When the test solute was replaced by water (hypo-osmotic solution), oocytes expressing AQP9 exhibited the same rapid swelling as for test solutes, suggesting that there is no discrimination between permeable solutes and water.
|
) which is an indicator of
the efficacy of a solute to induce osmosis was determined by simulation
of solute and water movement (Fig. 4, A and B)
using the Kedem and Katchalsky equations (Equations 1 and 2) for volume flow (Jv) and solute flux (Js)
(21, 22),
|
(Eq. 1) |
|
(Eq. 2) |
is the reflection coefficient of the test
solute; and Ci = ([Na+]in + [Cl]in) ([Na+]out + [Cl]out); 
p = ([test solute]in + [test solute]out)/2; and
cp = [test solute]in [test
solute]out. A value near unity indicates that the
solute elicits the full osmotic pressure, whereas a value near zero
indicates that the solute induces a negligible osmotic pressure. The
former is indicative of distinct pathways and the latter of a common
pathway for water and solute.
Mathematical simulation (23) according to the above equations, using
Pf values from hypotonic swelling experiments (Fig.
3D) and Ps values from tracer uptake
studies (Fig. 3A), revealed values that were close to
zero. (We did not use Ps values from iso-osmotic
assays (Fig. 4) because they are valid only when Jv
Js (24).) Most of the permeable solutes gave
values near zero (Fig. 4C). In contrast, oocytes
expressing AQP3 gave values close to unity for polyols larger than
glycerol (mannitol, threitol, and erythritol) and were close to zero
only for small polyols (glycerol and 1,3-propanediol). In experiments
with AQP1, was 1 for all solutes tested. These data substantiate
our claim that AQP9 has a common pathway for structurally unrelated
neutral solutes and water.
To define the selectivity of AQP9 in further detail, experiments were
performed using an osmotic lysis approach (Fig. 4D), in
which solutes (176 mosm) were tested for their ability to induce osmotic lysis under iso-osmotic conditions in oocytes expressing AQP9.
Osmotic lysis was induced by xylitol, erythritol, 1,3-propanediol, dimethylthiourea, and acetamide but not by raffinose, sucrose, methyl-D-glucopyranoside, glucose 6-phosphate, glycerol
3-phosphate, sodium or potassium gluconate, KCl, and choline chloride.
To test the possibility that AQP9 is a rectifying solute channel,
oocytes expressing AQP9 were exposed to hypertonic Barth's solutions
containing 1.0 M mannitol or 1.0 M NaCl. NaCl
induced shrinkage, whereas mannitol did not (data not shown),
supporting the concept that AQP9 is a symmetrical channel.
The discovery of AQP9 may now highlight the roles that members of the
aquaporin family could play in rapid movement of solutes across cell
membranes with minimal osmotic perturbation, particularly in tissues
that accumulate high levels of metabolites. The liver is a major site
of urea production, and a rapid urea exit mechanism is required, and
the lack of specialized urea transporters and selective functional
water channels in hepatocytes (1-3, 10) emphasizes the need of these
cells for AQP9 as an indiscriminate channel. In addition to urea, AQP9
may provide an exit route for purines and pyrimidines derived from
nucleotide synthesis de novo, ensuring the plentiful supply
of nucleotides to the brain, muscle, and hematopoietic tissues, in
which only a salvage pathway is available (25). Purine and pyrimidine
analogues such as 5-fluorouracil and 6-mercaptopurine are commonly used
as chemotherapeutic agents. AQP9 may indirectly affect the
chemosensitivity and resistance to these agents in cancer tissues.
Permeation of monocarboxylates such as lactate and -hydroxybutyrate
is necessary because liver is a major site of lactate utilization and
ketone body formation (5). Hepatocytes secrete lactate under hypoxic
conditions and export a large amount of ketone bodies such as
-hydroxybutyrate and acetoacetate induced by fasting or diabetic
conditions. Notably, AQP9 mRNA was up-regulated in liver from
streptozotocin-induced diabetic
rats.2
In summary, we report the first characterization of a broad
selectivity, neutral solute channel, AQP9, that permits solutes to
cross cell membranes rapidly and with minimal osmotic perturbation. The
observations from inhibition studies (Fig. 3F), and oocyte swelling assays (Fig. 4A), as well as the reflection
coefficients (Fig. 4C) strongly indicate that AQP9 provides
a common transmembrane pathway for both solutes and water. Our findings
have significant physiological implications, particularly in cells that
require absorption and excretion of large amounts of metabolites.
AQP9's indiscriminate nature, which allows passage of a wide range of structurally unrelated solutes, highlights its pharmacological relevance and the need for structural studies (27, 28) to elucidate the
molecular design of this unique promiscuous pore.
| |
FOOTNOTES |
|---|
* This work was supported in part by National Institutes of Health Grants DK46289 (to M. A. H.) and DK32753 (to W. B. G.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EMBL Data Bank with accession number(s) AF016406.
Supported by a Research Fellowship of the National Kidney
Foundation.
§ Supported by the Siriraj-China Medical Board, Mahidol University, Thailand.
¶ Samuel A. Levine Fellow of the American Heart Association, Massachusetts Affiliate.
Supported by National Institutes of Health Grant DK38452 (to
Dr. Dennis Brown).
§§ To whom correspondence should be addressed: Renal Division, Brigham & Women's Hospital, 77 Ave. Louis Pasteur, Boston MA 02115. Tel.: 617-525-5820; Fax: 617-525-5830; E-mail: mhediger{at}rics.bwh.harvard.edu.
The abbreviations used are: AQP, aquaporin; UT, urea transporter; kb, kilobase pairs.
2 H. Tsukaguchi and M. A. Hediger, unpublished data.
| |
REFERENCES |
|---|
|
Top
Abstract
Introduction
Materials & Methods
Results & Discussion
References
|
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  C Callies, T G Cooper, and C H Yeung Channels for water efflux and influx involved in volume regulation of murine spermatozoa Reproduction, October 1, 2008; 136(4): 401 - 410. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. M. Rodela, J. S. Ballantyne, and P. A. Wright Carrier-mediated urea transport across the mitochondrial membrane of an elasmobranch (Raja erinacea) and a teleost (Oncorhynchus mykiss) fish Am J Physiol Regulatory Integrative Comp Physiol, June 1, 2008; 294(6): R1947 - R1957. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. J. Wiegman, L. V. Bullinger, M. M. Kohlmeyer, T. C. Hunter, and M. J. Cipolla Regional Expression of Aquaporin 1, 4, and 9 in the Brain During Pregnancy Reproductive Sciences, May 1, 2008; 15(5): 506 - 516. [Abstract] [PDF]
|
|
|
|
 |
|
 A. Wellejus, H. E. Jensen, S. Loft, and T. E. Jonassen Expression of Aquaporin 9 in Rat Liver and Efferent Ducts of the Male Reproductive System After Neonatal Diethylstilbestrol Exposure J. Histochem. Cytochem., May 1, 2008; 56(5): 425 - 432. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T G Cooper, J P Barfield, and C H Yeung The tonicity of murine epididymal spermatozoa and their permeability towards common cryoprotectants and epididymal osmolytes Reproduction, May 1, 2008; 135(5): 625 - 633. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Pietrement, N. Da Silva, C. Silberstein, M. James, M. Marsolais, A. Van Hoek, D. Brown, N. Pastor-Soler, N. Ameen, R. Laprade, et al. Role of NHERF1, Cystic Fibrosis Transmembrane Conductance Regulator, and cAMP in the Regulation of Aquaporin 9 J. Biol. Chem., February 1, 2008; 283(5): 2986 - 2996. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. L. Lehmann, F. I. Carreras, L. R. Soria, S. A. Gradilone, and R. A. Marinelli LPS induces the TNF-{alpha}-mediated downregulation of rat liver aquaporin-8: role in sepsis-associated cholestasis Am J Physiol Gastrointest Liver Physiol, February 1, 2008; 294(2): G567 - G575. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. J. Yool Aquaporins: Multiple Roles in the Central Nervous System Neuroscientist, October 1, 2007; 13(5): 470 - 485. [Abstract] [PDF]
|
|
|
|
 |
|
 K. Matsumura, B. H.-J. Chang, M. Fujimiya, W. Chen, R. N. Kulkarni, Y. Eguchi, H. Kimura, H. Kojima, and L. Chan Aquaporin 7 Is a {beta}-Cell Protein and Regulator of Intraislet Glycerol Content and Glycerol Kinase Activity, {beta}-Cell Mass, and Insulin Production and Secretion Mol. Cell. Biol., September 1, 2007; 27(17): 6026 - 6037. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 E. Beitz Jammed traffic impedes parasite growth PNAS, August 28, 2007; 104(35): 13855 - 13856. [Full Text] [PDF]
|
|
|
|
 |
|
 K. Edashige, S. Ohta, M. Tanaka, T. Kuwano, D. M. Valdez Jr., T. Hara, B. Jin, S.-i. Takahashi, S. Seki, C. Koshimoto, et al. The Role of Aquaporin 3 in the Movement of Water and Cryoprotectants in Mouse Morulae Biol Reprod, August 1, 2007; 77(2): 365 - 375. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Liu, D. Promeneur, A. Rojek, N. Kumar, J. Frokiaer, S. Nielsen, L. S. King, P. Agre, and J. M. Carbrey Aquaporin 9 is the major pathway for glycerol uptake by mouse erythrocytes, with implications for malarial virulence PNAS, July 24, 2007; 104(30): 12560 - 12564. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. I. Carreras, G. L. Lehmann, D. Ferri, M. F. Tioni, G. Calamita, and R. A. Marinelli Defective hepatocyte aquaporin-8 expression and reduced canalicular membrane water permeability in estrogen-induced cholestasis Am J Physiol Gastrointest Liver Physiol, March 1, 2007; 292(3): G905 - G912. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Rojek, M. T. Skowronski, E.-M. Fuchtbauer, A. C. Fuchtbauer, R. A. Fenton, P. Agre, J. Frokiaer, and S. Nielsen Defective glycerol metabolism in aquaporin 9 (AQP9) knockout mice PNAS, February 27, 2007; 104(9): 3609 - 3614. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Ashutosh, S. Sundar, and N. Goyal Molecular mechanisms of antimony resistance in Leishmania J. Med. Microbiol., February 1, 2007; 56(2): 143 - 153. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 H.-F. Huang, R.-H. He, C.-C. Sun, Y. Zhang, Q.-X. Meng, and Y.-Y. Ma Function of aquaporins in female and male reproductive systems Hum. Reprod. Update, November 1, 2006; 12(6): 785 - 795. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Aharon and Z. Bar-Shavit Involvement of Aquaporin 9 in Osteoclast Differentiation J. Biol. Chem., July 14, 2006; 281(28): 19305 - 19309. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
B. Yang, D. Zhao, and A. S. Verkman Evidence against Functionally Significant Aquaporin Expression in Mitochondria J. Biol. Chem., June 16, 2006; 281(24): 16202 - 16206. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. Edashige, M. Tanaka, N. Ichimaru, S. Ota, K.-i. Yazawa, Y. Higashino, M. Sakamoto, Y. Yamaji, T. Kuwano, D. M. Valdez Jr., et al. Channel-Dependent Permeation of Water and Glycerol in Mouse Morulae Biol Reprod, April 1, 2006; 74(4): 625 - 632. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
N. Da Silva, C. Silberstein, V. Beaulieu, C. Pietrement, A. N. Van Hoek, D. Brown, and S. Breton Postnatal Expression of Aquaporins in Epithelial Cells of the Rat Epididymis Biol Reprod, February 1, 2006; 74(2): 427 - 438. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Amiry-Moghaddam, H. Lindland, S. Zelenin, B. A. Roberg, B. B. Gundersen, P. Petersen, E. Rinvik, I. A. Torgner, and O. P. Ottersen Brain mitochondria contain aquaporin water channels: evidence for the expression of a short AQP9 isoform in the inner mitochondrial membrane FASEB J, September 1, 2005; 19(11): 1459 - 1467. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. Kaufmann, J. C. Mathai, W. G. Hill, J. A. T. Dow, M. L. Zeidel, and J. L. Brodsky Developmental expression and biophysical characterization of a Drosophila melanogaster aquaporin Am J P |
, AQP1; 
, AQP9; 
, AQP3.
D, osmotic lysis assays of oocytes expressing AQP9. A range
of solutes was examined by observing osmotic lysis of oocytes under the
microscope 10 min after applying modified Barth's solution as
described in A. The radius (nm) of each substrate was
estimated from the molecular weight (Mr) and
density (
) (
× 3/4)1/3; +, oocytes lysed;