Angiotensin II stimulates vesicular H(+)-ATPase in rat proximal tubular cells

Two mechanisms of H(+) ion secretion in the proximal tubule that mediate bicarbonate reabsorption have been identified: the brush border Na/H exchanger and electrogenic H(+) ion secretion. Angiotensin II (AII) has been shown to be a regulator of the luminal Na(+)/H(+) exchanger and the basolateral Na(+)/HCO(3)(−) cotransporter. In the present study, we examined the effects of AII on H(+)-ATPase activity in isolated proximal tubule fragments. H(+)-ATPase activity was assessed by monitoring intracellular pH after Na(+) removal from the bath. In addition, we investigated the effects on pH recovery of the proton pump inhibitor bafilomycin A(1), removal of Cl(−), and of colchicine. pH was continuously measured with the pH-sensitive fluorescent dye 2′, 7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Recovery of cell pH was observed in the absence of external Na(+) and was significantly accelerated by AII. The AII-stimulated pH recovery was completely abolished by bafilomycin A(1), by removal of Cl(−), by NPPB [5-nitro-2-(3-phenylpropylamino)-benzoate; a potent Cl(−) channel blocker], and by colchicine. We conclude from these studies that AII stimulates proton extrusion via H(+)-ATPase by a Cl(−)-dependent process involving brush border insertion of vesicles. This process may contribute to up-regulation of HCO(3)(−) reabsorption along the proximal tubule when tubules are exposed to AII.