Effect of apical bath CO2 on apical membrane Na/2HCO3 cotransporter. (A) 0.5 mM DIDS was added to the apical bath to obtain initial control response. The DIDS-induced response was then obtained in the presence of 13% apical bath CO2. After washout with control Ringer, DIDS was added to the apical bath to obtain the final control response. (B) 13% CO2-equilibrated Ringer was perfused into the apical bath to record the initial control response. This maneuver was repeated in the presence of 0.5 mM of apical DIDS. After DIDS washout, 13% apical CO2-induced control response was obtained. Solid bars above the graphs represent solution changes from control Ringer as described in the legend to Fig. 2.