Regulation of inwardly rectifying K+ channels by intracellular pH in opossum kidney cells

The effects of intracellular pH on an inwardly rectifying K⁺ channel (K_in channel) in opossum kidney (OK) cells were examined using the patch-clamp technique. Experiments with inside-out patches were first carried out in Mg²⁺-and adenosine triphosphate (ATP)-free conditions, where Mg²⁺-induced inactivation and ATP-induced reactivation of K_in channels were suppressed. When the bath (cytoplasmic side) pH was decreased from 7.3 to either 6.8 or 6.3, K_in channels were markedly inhibited. The effect of acid pH was not fully reversible. When the bath pH was increased from 7.3 to 7.8, 8.3 or 8.8, the channels were activated reversibly. The channel activity exhibited a sigmoidal pH dependence with a maximum sensitivity at pH 7.5. Inside-out experiments were also carried out with a solution containing 3 mM Mg-ATP and a similar pH sensitivity was observed. However, in contrast with the results obtained in the absence of Mg²⁺ and ATP, the effect of acid pH was fully reversible. Experiments with cell-attached patches demonstrated that changes in intracellular pH, which were induced by changing extracellular pH in the presence of an H⁺ ionophore, could influence the channel activity reversibly. It is concluded that the activity of K_in channels can be controlled by the intracellular pH under physiological conditions.