Comparison of Na+/H+ and Cl-/OH- exchange in rat jejunal brush border membrane vesicles: studies with acridine orange.

Vesicles can accumulate the fluorescent dye acridine orange if their intravesicular space is acidic compared with the external one. The quenching of the acridine orange fluorescence was used to monitor the formation and the dissipation of a delta pH in brush border vesicles isolated from rat kidney cortex or rat jejunum. Similar findings were obtained with both brush border membrane vesicles preparations. Under condition of potassium efflux, acridine orange fluorescence was quenched only in the presence of valinomycin showing a H+ greater than K+ conductance. Under condition of sodium efflux, an acidification of the intravesicular space occurred due to: a) indirect (electrical) coupling of sodium and proton fluxes; b) directly coupled Na+/H+ exchange. It is possible to preseta delta pH across the vesicles (pHin less than pHout) and to monitor the rate of the delta pH dissipation. The initial rate of dissipation of a preset delta pH was accelerated in a saturable manner by pulse-injections of sodium, this phenomenon is sensitive to the inhibition of Amiloride; Lithium can partially replace sodium. An inwardly directed chloride gradient did not induce an appreciable intravesicular acidification. On the other hand a Na-gluconate (in greater than out) gradient and a similar NaCl gradient produced the same intravesicular acidification. Furthermore the initial rate of dissipation of a preset delta pH was accelerated for the same extent by pulse injections of Na-gluconate and NaCl. These findings clearly confirm the existence of the Na+/H+ exchange. In contrast the Cl-/OH- exchange, if at all present, operates, in these brush border membrane preparation, at a much lower rate than Na+/H+ exchange.