Early and late activation of the voltage-gated proton channel during lactic acidosis through pH-dependent and -independent mechanisms.

Voltage-gated proton (H+) channels play a pivotal role in compensating charge and pH imbalances during respiratory bursts in phagocytes. Lactic acidosis is a clinically important metabolic condition accompanying various tissue disorders in which the extracellular pH and the intracellular pH often change in parallel. In this study, we investigated the responses of the H+ channel in microglia to lactate-induced pH disturbances using the perforated-patch recordings. Na-lactate (pH 6.8) acidified the cells and activated the H+ channel within 5 min. This early activation was correlated with increases in the pH gradient across the plasma membrane (DeltapH) and was dose-dependent over a concentration range of 10-150 mM. At 10 mM, the change in DeltapH was only slight, but the H+ currents continued to increase over an hour after the cell acidosis was stabilized. Prolonged exposure to lactate (10-20 mM, >1 h) increased the amplitude by two to threefold. The late activation was not explained by increased DeltapH but by changes in the property of the channel per se. Pretreatment with staurosporine and chelerythrine, inhibitors for protein kinase C, prevented the late activation. These results suggest that the H+ channel could be activated greatly during long-lasting lactic acidosis through both DeltapH-dependent and -independent mechanisms.