Potassium/proton exchange in brush-border membrane of rat ileum

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Abstract
Summary These experiments were designed to determine whether proton-driven86Rb uptake was present in apical membrane vesicles prepared from rat ileum. The uptake of86Rb was approximately 300 to 350% greater in the presence of a 100-fold H+ gradient than in its absence and was greater at 1, 2 and 5 minutes (“overshoot”) than that at 90 minutes. Proton-driven86Rb uptake was decreased by 20% in TMA-nitrate compared to that in TMA-gluconate. 0.3mm amiloride did not significantly inhibit proton-driven86Rb uptake; in contrast, proton-driven22Na uptake was significantly inhibited by 0.3mm amiloride by 34%. Similarly, 25mm KCl inhibited proton-driven86Rb uptake more than that of22Na, while the inhibition of proton-driven22Na uptake by 25mm NaCl was greater than that of86Rb. In additional studies intravesicular acidification measured by acridine orange fluorescence was demonstrated in the presence of an out-wardly directed K gradient. These studies demonstrate that a proton gradient stimulates86Rb uptake and a K gradient induces intravesicular acidification; and that these fluxes are mediated by a K/H exchange distinct from Na/H exchange which is also present in this membrane. We conclude that a specific exchange process for K/H is located in ileal apical membrane vesicles.