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

Publisher Website
Google Scholar
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.