Na/H- and Cl/OH-exchange in rat jejunal and rat proximal tubular brush border membrane vesicles

Abstract

The quenching of the acridine orange fluorescence was used to monitor the formation and/or dissipation of a Δ pH in brush border vesicles isolated from rat kidney cortex or rat jejunum. Similar findings were obtained with both brush border membrane vesicle preparations. Acridine orange fluorescence was quenched by a preset Δ pH (intravesicular acid) or by the ionophore (valinomycin/CCCP) dependent development of a Δ pH (intravesicular acid) under conditions of potassium efflux. Under sodium efflux conditions, an acidification of the intravesicular space occurred: a) due to indirect (electrical) coupling of sodium and proton fluxes; b) due to directly coupled sodium/proton exchange. The initial rate of the dissipation of a preset Δ pH was accelerated by pulse injections of sodium in a saturable manner; lithium partially replaced sodium. The sodium dependent acceleration in the rate of dissipation of a preset Δ pH was not altered by replacing gluconate with chloride. Amiloride was an inhibitor of directly coupled sodium/proton exchange. An inwardly directed chloride gradient did not induce intravesicular acidification. The initial rate of the dissipative proton fluxes (preset Δ pH) was slightly accelerated by an outwardly directed chloride gradient. Sodium/proton exchange dependent acidification of the intravesicular space was not altered by replacing gluconate with chloride. These results clearly document the existence of sodium/proton exchange in both renal and intestinal brush border membrane vesicles. In contrast, Cl/OH exchange — under our experimental conditions — must have a much smaller rate than Na/H exchange.