Fig. 3. Time courses of the transepithelial voltage normalized to the percentage of the control value (–38 mV and –19 mV, respectively), showing the effects of substitution of Na⁺ (time period 1, N-methylglucamine) and Cl^- (time period 2, gluconate). During the time periods indicated by w, perfusion of the anterior stomach preparation was changed to withdrawal mode, establishing the bathing solution also on the luminal side of the epithelium. Infusion mode was used during the rest of the time. At the arrow, the preparation was withdrawn from the perfusion pipette.