Ouabain-insensitive K-adenosine triphosphatase in distal nephron segments of the rabbit

An electrogenic H-ATPase sensitive to inhibition by N-ethyl-maleimide has been reported to be present in renal distal tu-bules. In contrast to another H-ATPase (gastric H-K-ATP-ase), the renal enzyme is not stimulated by K+ and is not inhib-ited 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 ab-sence of KCI 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 oxida-tion of NADH. There was a significant K-ATPase activity (expressed as pmol * min- ' * mm-') in the connecting tubule (CNT, 17.0±33), 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-ATP-ase. However, the physiological role of K-ATPase in the distal nephron segments remains to be elucidated