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Papers In Press, published online ahead of print January 11, 2005
Department of Medicine, University of Texas Medical Branch, Galveston, TX 77555-0562
Corresponding Author: dgood{at}utmb.edu
In the renal medullary thick ascending limb (MTAL), inhibiting the basolateral NHE1 Na+/H+ exchanger with amiloride or nerve growth factor (NGF) results secondarily in inhibition of the apical NHE3 Na+/H+ exchanger, thereby decreasing transepithelial HCO3- absorption. MTALs from rats were studied by in vitro microperfusion to identify the mechanism underlying cross-talk between the two exchangers. Basolateral addition of 10
J. Biol. Chem, 10.1074/jbc.M410719200
Submitted on September 17, 2004
Revised on December 20, 2004
Accepted on January 11, 2005
The basolateral NHE1 Na+/H+ exchanger regulates transepithelial HCO3-absorption through actin cytoskeleton remodeling in renal thick ascending limb
M amiloride or 0.7 nM NGF decreased HCO3- absorption by 27-32%. Jasplakinolide, which stabilizes F-actin, or latrunculin B, which disrupts F-actin, decreased basal HCO3- absorption by 30% and prevented the inhibition by amiloride or NGF. Jasplakinolide had no effect on HCO3- absorption in tubules bathed with amiloride or a Na+-free bath to inhibit NHE1. Jasplakinolide and latrunculin B did not prevent inhibition of HCO3- absorption by vasopressin or stimulation by hyposmolality, factors that regulate HCO3- absorption through primary effects on apical Na+/H+ exchange. Treatment of MTALs with amiloride or NGF for 15 min decreased polymerized actin with no change in total cell actin, as assessed both by fluorescence microscopy and by actin Triton X-100 solubility. Jasplakinolide prevented the amiloride-induced actin remodeling. Vasopressin, which inhibits HCO3- absorption by an amount similar to that observed with amiloride and NGF but does not act via NHE1, did not affect cellular F-actin content. These results indicate that basolateral NHE1 regulates apical NHE3 and HCO3- absorption in the MTAL by controlling the organization of the actin cytoskeleton.
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