Figure 8. Effect of intravesicular membrane potential on Na-HCO₃ cotransport activities in basolateral membrane vesicles from proximal colon.

Intravesicular positive membrane potential [generated using inward K⁺ gradient and valinomycin (Val)] dependent HCO₃-gradient-driven ²²Na (0.1 mM) uptake was measured as described in the Method section both in presence and absence of 1 mM amiloride. Intravesicular positive potential stimulated amiloride-insensitive HCO₃ gradient-driven ²²Na uptake. Intravesicular positive potential did not affect amiloride-sensitive Na-HCO₃ cotransport. Uptake obtained in presence of amiloride represented amiloride-insensitive uptake, while amiloride-sensitive uptake was calculated by subtracting the amiloride-insensitive uptake from that of uptake in the absence of amiloride. *p<0.001 compared to –Val in amiloride-insensitive; **p<0.05 compared to –Val in amiloride-sensitive.