title: In rat inner medullary collecting duct, NH uptake by the Na,K-ATPase is increased during hypokalemia.
abstract: In rat terminal inner medullary collecting duct (tIMCD), the Na,K-ATPase mediates NH uptake, which increases secretion of net H(+) equivalents. K(+) and NH compete for a common binding site on the Na,K-ATPase. Therefore, NH uptake should increase during hypokalemia because interstitial K(+) concentration is reduced. We asked whether upregulation of the Na,K-ATPase during hypokalemia also increases basolateral NH uptake. To induce hypokalemia, rats ate a diet with a low K(+) content. In tIMCD tubules from rats given 3 days of dietary K(+) restriction, Na,K-ATPase beta(1)-subunit (NK-beta(1)) protein expression increased although NK-alpha(1) protein expression and Na,K-ATPase activity were unchanged relative to K(+)-replete controls. However, after 7 days of K(+) restriction, both NK-alpha(1) and NK-beta(1) subunit protein expression and Na,K-ATPase activity increased. The magnitude of Na,K-ATPase-mediated NH uptake across the basolateral membrane (J) was determined in tIMCD tubules perfused in vitro from rats after 3 days of a normal or a K(+)-restricted diet. J was the same in tubules from rats on either diet when measured at the same extracellular K(+) concentration. However, in either treatment group, increasing K(+) concentration from 10 to 30 mM reduced J >60%. In conclusion, with 3 days of K(+) restriction, NH uptake by Na,K-ATPase is increased in the tIMCD primarily from the reduced interstitial K(+) concentration.
authors.affiliation: University of Texas, Medical School at Houston, Houston, Texas 77030, USA. susan.m.wall@uth.tmc.edu
authors.forename: Susan M
authors.initials: SM
authors.lastname: Wall
authors.forename: Michael P
authors.initials: MP
authors.lastname: Fischer
authors.forename: Gheun-Ho
authors.initials: GH
authors.lastname: Kim
authors.forename: Bich-May
authors.initials: BM
authors.lastname: Nguyen
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Hassell
mesh_terms: D000818:Animals; D015971:Gene Expression Regulation, Enzymologic; D007008:Hypokalemia / Q000378:metabolism*; D007679:Kidney Medulla / Q000201:enzymology*; D007685:Kidney Tubules, Collecting / Q000201:enzymology*; D008297:Male; D017419:Potassium, Dietary / Q000493:pharmacokinetics; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
chemical_list: D017419:Potassium, Dietary; D000644:Quaternary Ammonium Compounds; D000254:Sodium-Potassium-Exchanging ATPase