The effect of cyanide on apparent potassium conductance across the peritubular cell membrane of frog proximal tubules

Abstract

To test for the effect of cyanide on frog proximal renal tubules the potential difference across the peritubular cell membrane (PDpt) has been recorded continuously before and during peritubular application of 1 mmol/l cyanide using conventional microelectrodes.

Before application of cyanide PDpt amounts to −61.5 ±2.2 mV in the absence of luminal substrate. Cyanide depolarizes the peritubular cell membrane by +18.8±2.3 mV/10 min in the presence and by +4.5±0.9 mV/10 min in the absence of luminal substrate. The rapid depolarization of the cell membranes to addition of glucose to luminal perfusate is not significantly influenced by exposure to cyanide, whereas the influence of altered peritubular potassium concentration (from 3 to 9 mmol/l) is significantly reduced from +15.2±1.7 mV to +8.7±1.8 mV. Following exposure to cyanide the lumped resistance of the luminal and peritubular cell membranes increases significantly by 36±7%/6 min, and the cellular core resistance significantly by 14±6%/6 min. As a result, cyanide markedly decreases the peritubular potassium conductance, depolarizes the cell membranes and reduces the driving force for sodium coupled transport processes. Thus cyanide fully mimicks the effects of ouabain, although cyanide in contrast to ouabain is expected to deplete the cells from ATP. In conclusion ATP/ADP is not likely to play a major role in the regulation of sodium coupled transport processes and peritubular potassium conductance in amphibian proximal tubules.