title: The basolateral NHE1 Na+/H+ exchanger regulates transepithelial HCO3- absorption through actin cytoskeleton remodeling in renal thick ascending limb.
abstract: 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. The basolateral addition of 10 microM 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 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.
authors.affiliation: Department of Medicine, University of Texas Medical Branch, Galveston, Texas 77555-0562, USA.
authors.forename: Bruns A
authors.initials: BA
authors.lastname: Watts
authors.forename: Thampi
authors.initials: T
authors.lastname: George
authors.forename: David W
authors.initials: DW
authors.lastname: Good
mesh_terms: D000042:Absorption; D000199:Actins / Q000502:physiology*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D003078:Colchicine / Q000494:pharmacology; D047630:Depsipeptides / Q000494:pharmacology; D004848:Epithelium / Q000378:metabolism; D008138:Loop of Henle / Q000378:metabolism*; D008297:Male; D020932:Nerve Growth Factor / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology*; D012995:Solubility; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines
chemical_list: D000199:Actins; D001639:Bicarbonates; D019086:Bridged Bicyclo Compounds, Heterocyclic; D047630:Depsipeptides; C452850:Slc9a1 protein, rat; C000613387:Slc9a3 protein, rat; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D013844:Thiazoles; D053778:Thiazolidines; C057531:jasplakinolide; D000584:Amiloride; D020932:Nerve Growth Factor; D012964:Sodium; C037068:latrunculin B; D003078:Colchicine