Proton modulation of outward K+ currents in interferon-gamma-activated microglia

Whole-cell outward potassium currents (I-K) were measured in interferon (IFN)-gamma-activated cultured murine microglial cells. Acidification of the external milieu moved the threshold of activation of IK in a depolarizing direction, while alkalinization showed the opposite effect. A shift of more than 20 mV of the steady-state activation and inactivation curves of I-K in hyperpolarizing direction was measured when pH was changed from 5.8 to 7.8. The time-dependent inactivation of I-K was slower when superfusing cells with acid solutions than with alkaline ones. In contrast, variations in the pH of the intracellular solution did not alter kinetics of I-K. However, alkalinization of the internal solution from a pH of 5.8 to 7.8 led to a two-fold increase in the current density of I-K.