Fused cells of frog proximal tubule: II. Voltage-dependent intracellular pH

Experiments were performed in intact proximal tubules of the doubly perfused kidney and in fused proximal tubule cells of Raha esculenta to evaluate the dependence of intracellular pH (pH_i) on cell membrane potential applying pH-sensitive and conventional microelectrodes. In proximal tubules an increase of the K^- concentration in the peritubular perfusate from 3 to 15 mmol/liter decreased the peritubular cell membrane potential from -55±2 to -38±1 mV paralleled by an increase of pH_i, from 7.54±0.02 to 7.66±0.02. The stilbene derivative DIDS hyperpolarized the cell membrane potential from -57 ± 2 to -71 ±4 mV and led to a significant increase of the K^--induced cell membrane depolarization, but prevented the K^--induced intracellular alkalinization. Fused proximal tubule cells were impaled by three microelectrodes simultaneously and cell voltage was clamped stepwise while pH_i changes were monitored. Cell membrane hyperpolarization acidified the cell cytoplasm in a linear relationship. This voltage-induced intracellular acidification was reduced to about one-third when HCO₃ ions were omitted from the extracellular medium. We conclude that in proximal tubule cells pH_i depends on cell voltage due to the rheogenicity of the HCO₃^- transport system.