title: Ouabain-insensitive K-adenosine triphosphatase in distal nephron segments of the rabbit.
abstract: An electrogenic H-ATpase sensitive to inhibition by N-ethyl-maleimide has been reported to be present in renal distal tubules. In contrast to another H-ATPase (gastric H-K-ATPase), the renal enzyme is not stimulated by K+ and is not inhibited by vanadate. However, our preliminary observations indicated that a K-stimulated ATPase (K-ATPase) sensitive to inhibition by vanadate is present in renal medullary collecting duct (MCD). To localize and further characterize this renal tubular K-ATPase, we measured K-ATPase activity in eight specific segments of the rabbit nephron. K-ATPase activity was the difference in ATPase activity in the presence and absence of KCl but in the presence of ouabain (to inhibit Na-K-ATPase). ATPase activity was determined by a fluorometric microassay in which ATP hydrolysis is coupled to the oxidation of NADH. There was a significant K-ATPase activity (expressed as pmol.min-1.mm-1) in the connecting tubule (CNT, 17.0 +/- 3.3), cortical collecting duct (CCD, 6.6 +/- 0.7), and MCD (8.8 +/- 1.7), but not in the proximal segments and the thick ascending limbs. The renal tubular K-ATPase was not only inhibited by vanadate but also by omeprazole and SCH 28080 (relatively specific inhibitors of gastric H-K-ATPase). It is concluded that K-ATPase present in the CNT, CCD, and MCD has some properties in common with gastric H-K-ATPase. However, the physiological role of K-ATPase in the distal nephron segments remains to be elucidated.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville 32610.
authors.forename: L C
authors.initials: LC
authors.lastname: Garg
authors.forename: N
authors.initials: N
authors.lastname: Narang
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D027682:Cation Transport Proteins; D017506:H(+)-K(+)-Exchanging ATPase; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D007684:Kidney Tubules / Q000201:enzymology*; D007686:Kidney Tubules, Distal / Q000201:enzymology*; D009853:Omeprazole / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*; D011817:Rabbits; D012965:Sodium Chloride / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase; D014638:Vanadates / Q000494:pharmacology
chemical_list: D027682:Cation Transport Proteins; D007093:Imidazoles; C035235:Sch 28080; D014638:Vanadates; D012965:Sodium Chloride; D010042:Ouabain; D000251:Adenosine Triphosphatases; C022761:potassium transporting ATPase; D017506:H(+)-K(+)-Exchanging ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D009853:Omeprazole