Inhibition of the human intermediate conductance Ca²⁺-activated K⁺ channel, hIK1, by volatile anesthetics

Ca²⁺-activated K⁺ channels (K(Ca)) regulate a wide variety of cellular functions by coupling intracellular Ca²⁺ concentration to membrane potential. There are three major groups of K(Ca) classified by their unit conductances: large (BK), intermediate (IK), and small (SK) conductance of channels. BK channel is gated by combined influences of Ca²⁺ and voltage, while IK and SK channels are gated solely by Ca²⁺. Volatile anesthetics inhibit BK channel activity by interfering with the Ca²⁺ gating mechanism. However, the effects of anesthetics on IK and SK channels are unknown. Using cloned IK and SK channels, hIK1 and hSK1-3, respectively, we found that the currents of hIK1 were inhibited rapidly and reversibly by volatile anesthetics, whereas those of SK channels were not affected. The IC₅₀ values of the volatile anesthetics, halothane, sevoflurane, enflurane, and isoflurane for hIK1 inhibition were 0.69, 0.42, 1.01 and 1.03 mM, respectively, and were in the clinically used concentration range. In contrast to BK channel, halothane inhibition of hIK1 currents was independent of Ca²⁺ concentration, suggesting that Ca²⁺ gating mechanism is not involved. These results demonstrate that volatile anesthetics, such as halothane, enflurane, isoflurane, and sevoflurane, affect BK, IK, and SK channels in distinct ways. Copyright (C) 2000.