title: Apical membrane localization of ouabain-sensitive K(+)-activated ATPase activities in rat distal colon.
abstract: This study sought to establish the presence of K(+)-activated adenosinetriphosphatase (ATPase) activity in the colonic mucosa of the rat distal colon. K(+)-activated ATPase activity was present in apical membranes but not in basolateral membranes. K(+)-activated ATPase activity in apical membranes represented an approximate 10-fold enrichment compared with that in the homogenate. Na(+)-K(+)-activated ATPase activity was also present in homogenate but was enriched less than fourfold in apical membranes. K(+)-activated ATPase activity in apical membranes had both ouabain-sensitive and ouabain-insensitive components. In contrast, Na(+)-K(+)-activated ATPase activity was completely inhibited by ouabain. Similar half-maximal concentrations for K+ and pH activation curves were found for both ouabain-sensitive and ouabain-insensitive fractions. In addition to K+, the ouabain-sensitive fraction of K(+)-activated ATPase activity was stimulated by Rb+, NH+4, and Cs+, whereas the ouabain-insensitive fraction was activated only by Rb+. K(+)-activated ATPase activity was significantly inhibited by vanadate but not by N-ethylmaleimide or omeprazole. In the proximal colon, in contrast to the distal colon, active K+ absorption is not present, and K(+)-activated ATPase is approximately 20% of that in the distal colon. These studies demonstrate that K(+)-activated ATPase is present in apical membranes of rat distal colon and permit the speculation that this enzyme represents a unique and distinct ATPase (compared with either Na(+)-K(+)-ATPase or gastric parietal cell K(+)-ATPase) and is likely linked closely to the active K+ absorptive process present in this epithelium.
authors.affiliation: Department of Internal Medicine, Yale University, New Haven, Connecticut 06510.
authors.forename: J R
authors.initials: JR
authors.lastname: Del Castillo
authors.forename: V M
authors.initials: VM
authors.lastname: Rajendran
authors.forename: H J
authors.initials: HJ
authors.lastname: Binder
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D027682:Cation Transport Proteins; D002412:Cations / Q000378:metabolism; D002462:Cell Membrane / Q000201:enzymology; D003106:Colon / Q000201:enzymology* / Q000648:ultrastructure; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000201:enzymology* / Q000648:ultrastructure; D008274:Magnesium / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase
chemical_list: D027682:Cation Transport Proteins; D002412:Cations; D010042:Ouabain; D012964:Sodium; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; C022761:potassium transporting ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium