title: Ouabain-sensitive H,K-ATPase functions as Na,K-ATPase in apical membranes of rat distal colon.
abstract: Na,K-ATPase activity has been identified in the apical membrane of rat distal colon, whereas ouabain-sensitive and ouabain-insensitive H,K-ATPase activities are localized solely to apical membranes. This study was designed to determine whether apical membrane Na,K-ATPase represented contamination of basolateral membranes or an alternate mode of H,K-ATPase expression. An antibody directed against the H, K-ATPase alpha subunit (HKcalpha) inhibited apical Na,K-ATPase activity by 92% but did not alter basolateral membrane Na,K-ATPase activity. Two distinct H,K-ATPase isoforms exist; one of which, the ouabain-insensitive HKcalpha, has been cloned. Because dietary sodium depletion markedly increases ouabain-insensitive active potassium absorption and HKcalpha mRNA and protein expression, Na, K-ATPase and H,K-ATPase activities and protein expression were determined in apical membranes from control and sodium-depleted rats. Sodium depletion substantially increased ouabain-insensitive H, K-ATPase activity and HKcalpha protein expression by 109-250% but increased ouabain-sensitive Na,K-ATPase and H,K-ATPase activities by only 30% and 42%, respectively. These studies suggest that apical membrane Na,K-ATPase activity is an alternate mode of ouabain-sensitive H,K-ATPase and does not solely represent basolateral membrane contamination.
authors.affiliation: Department of Internal Medicine, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: V M
authors.initials: VM
authors.lastname: Rajendran
authors.forename: P
authors.initials: P
authors.lastname: Sangan
authors.forename: J
authors.initials: J
authors.lastname: Geibel
authors.forename: H J
authors.initials: HJ
authors.lastname: Binder
mesh_terms: D000818:Animals; D015153:Blotting, Western; D003106:Colon / Q000201:enzymology*; D004039:Diet, Sodium-Restricted; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D017506:H(+)-K(+)-Exchanging ATPase / Q000737:chemistry / Q000502:physiology*; D008566:Membranes / Q000201:enzymology; D010042:Ouabain / Q000494:pharmacology*; D020033:Protein Isoforms; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D020033:Protein Isoforms; D010042:Ouabain; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase