DIDS-sensitive Na/2HCO₃ cotransporter at the apical membrane. (A) 0.5 mM DIDS was added to the apical bath to obtain initial control response (pH_i, TEP, and R_T). The DIDS-induced response was then obtained in the presence of low (2.62 mM) HCO₃ Ringer in the apical bath. After washout with control Ringer, DIDS was added to the apical bath to obtain the final control response. (B) Low HCO₃ (2.62 mM) Ringer was perfused into the apical bath to obtain initial control response. The low basal bath [HCO₃]-induced response was then obtained in the presence of 0.5 mM of apical DIDS. After DIDS washout, low basal bath [HCO₃]-induced control response was obtained. Solid bars above the graphs represent solution changes from control Ringer as described in the legend to Fig. 2.