title: Nongenomic regulation by aldosterone of the epithelial NHE3 Na(+)/H(+) exchanger.
abstract: The relevance of nongenomic pathways to regulation of epithelial function by aldosterone is poorly understood. Recently, we demonstrated that aldosterone inhibits transepithelial HCO(3)(-) absorption in the renal medullary thick ascending limb (MTAL) through a nongenomic pathway. Here, we examined the transport mechanism(s) responsible for this regulation, focusing on Na(+)/H(+) exchangers (NHE). In the MTAL, apical NHE3 mediates H(+) secretion necessary for HCO(3)(-) absorption; basolateral NHE1 influences HCO(3)(-) absorption by regulating apical NHE3 activity. In microperfused rat MTALs, the addition of 1 nM aldosterone rapidly decreased HCO(3)(-) absorption by 30%. This inhibition was unaffected by three maneuvers that inhibit basolateral Na(+)/H(+) exchange and was preserved in MTALs from NHE1 knockout mice, ruling out the involvement of NHE1. In contrast, exposure to aldosterone for 15 min caused a 30% decrease in apical Na(+)/H(+) exchange activity over the intracellular pH range from 6.5 to 7.7, due to a decrease in V(max). Inhibition of HCO(3)(-) absorption by aldosterone was not affected by 0.1 mM lumen Zn(2+) or 1 mM lumen DIDS, arguing against the involvement of an apical H(+) conductance or apical K(+)-HCO(3)(-) cotransport. These results demonstrate that aldosterone inhibits HCO(3)(-) absorption in the MTAL through inhibition of apical NHE3, and identify NHE3 as a target for nongenomic regulation by aldosterone. Aldosterone may influence a broad range of epithelial transport functions important for extracellular fluid volume and acid-base homeostasis through direct regulation of this exchanger.
authors.affiliation: 4.200 John Sealy Annex, The University of Texas Medical Branch, 301 University Blvd., Galveston, TX 77555-0562, USA. dgood@utmb.edu
authors.forename: David W
authors.initials: DW
authors.lastname: Good
authors.forename: Thampi
authors.initials: T
authors.lastname: George
authors.forename: Bruns A
authors.initials: BA
authors.lastname: Watts
mesh_terms: D000450:Aldosterone / Q000494:pharmacology*; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism*; D008138:Loop of Henle / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D051381:Rats; D017207:Rats, Sprague-Dawley; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; C000613386:Slc9a3 protein, mouse; C000613387:Slc9a3 protein, rat; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000450:Aldosterone