The electrical profile of the distal tubule in Triturus kidney

The transepithelial potential difference (VTE) and transepithelial resistance (RTE) were determined along the length of the distal tubule of the amphibian Triturus alpestris. The site of impalements was determined at the end of each experiment by latex injection and microdissection. Two segments, differing by their distribution at the surface of the kidney, by their respective diameters and by their electrical properties could be identified: the early distal tubule (EDT) and the late distal tubule (LDT). VTE was invariably positive in the EDT; it increased from approximately + 5 mV to approximately + 22 mV within the first 30% of this segment and remained roughly constant distally to this site. RTE was estimated at 57 omega X cm2 in the EDT. The LDT exhibited essentially negative VTE figures with the exception of its very initial portion; the peak negativity at the end of the LDT was -35 mV. RTE was assessed from 8 measurements performed in the first 30% of the LDT; the tentative transepithelial resistance was 530 omega X cm2. Provisional evidence suggests that the transepithelial resistance of the terminal portion of the LDT may be substantially larger than the resistance measured in other parts of this segment.