Figure 7. DIDS-inhibition kinetics of Na-HCO₃ cotransport activities in basolateral membrane vesicles from proximal colon.

Increasing DIDS concentrations inhibit both amiloride-insensitive and amiloride-sensitive proton/HCO₃ gradient-driven ²²Na uptake with half maximal inhibitory concentration (Ki) of approximately 8.9±1.2 and 263.8±26.4 µM, respectively. Proton/HCO₃ gradient-driven ²²Na uptake (0.1 mM) was measured as described in the Method section with increasing extravesicular DIDS concentrations both in presence and absence of inhibitors (either 100 µM EIPA or 1 µM HOE694). Uptake obtained in presence of amiloride represented amiloride-insensitive proton/HCO₃ gradient-driven uptake. Amiloride-sensitive uptake (which also includes HOE694 sensitive Na-H exchange) was calculated by subtracting uptake obtained in presence of EIPA from that of uptake in the absence of inhibitors. HOE694-sensitive uptake was calculated by subtracting uptake obtained in presence of HOE694 from that of uptake in the absence of inhibitors. Amiloride-sensitive proton/HCO₃ gradient-driven uptake was calculated by subtracting HOE694-sensitive uptake from that of EIPA-sensitive uptake. The inhibitory constants were calculated using a nonlinear regression with the EnzFitter software (Biosoft, Cambridge, UK).