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+/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 A(1), removal of Cl-, and of colchicine. pH was continuously measured with the pa-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 HCO3- reabsorption along the proximal tubule when tubules are exposed to AII.