Fig. 5. Time courses of the transepithelial voltage normalized to the percentage of the control value (–46 mV and –22 mV, respectively), showing the effects of ouabain (2.5 mmol l^-1) during time period 1, of BaCl₂ (5 mmol l^-1) during time period 2 and of amiloride (0.2 mmol l^-1) during time period 3. During the time period denoted w, perfusion of the 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.