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J. Biol. Chem., Vol. 280, Issue 12, 11439-11447, March 25, 2005

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The Basolateral NHE1 Na⁺/H⁺ Exchanger Regulates Transepithelial Absorption through Actin Cytoskeleton Remodeling in Renal Thick Ascending Limb^*

Bruns A. Watts, III, Thampi George, and David W. Good

From the Departments of Medicine and Neuroscience and Cell Biology, University of Texas Medical Branch, Galveston, Texas 77555

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 absorption. MTALs from rats were studied by in vitro microperfusion to identify the mechanism underlying cross-talk between the two exchangers. The basolateral addition of 10 µM amiloride or 0.7 nM NGF decreased absorption by 27-32%. Jasplakinolide, which stabilizes F-actin, or latrunculin B, which disrupts F-actin, decreased basal absorption by 30% and prevented the inhibition by amiloride or NGF. Jasplakinolide had no effect on absorption in tubules bathed with amiloride or a Na⁺-free bath to inhibit NHE1. Jasplakinolide and latrunculin B did not prevent inhibition of absorption by vasopressin or stimulation by hyposmolality, factors that regulate 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 amiloride-induced actin remodeling. Vasopressin, which inhibits 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 absorption in the MTAL by controlling the organization of the actin cytoskeleton.

Received for publication, September 17, 2004 , and in revised form, December 20, 2004.

^* This work was supported by National Institutes of Health Grant DK-38217 and by a grant from the John Sealy Memorial Endowment Fund for Biomedical Research. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

To whom correspondence should be addressed: 4.200 John Sealy Annex, University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0562. Tel.: 409-772-2472; Fax: 409-772-5451; E-mail: dgood{at}utmb.edu.

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