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

Abstract

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+/HCO3−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 A1, 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 A1, 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 HCO3−reabsorption along the proximal tubule when tubules are exposed to AII.