Novel Activation of Voltage-gated K+ Channels by Sevoflurane

Abstract

Halogenated inhaled anesthetics modulate voltage-gated ion channels by unknown mechanisms. Biophysical analyses revealed novel activation of K(v) channels by the inhaled anesthetic sevoflurane. K(v) channel activation by sevoflurane results from the positive allosteric modulation of activation gating. The unique activation of K(v) channels by sevoflurane demonstrates novel anesthetic specificity and offers new insights into allosteric modulation of channel gating. Voltage-gated ion channels are modulated by halogenated inhaled general anesthetics, but the underlying molecular mechanisms are not understood. Alkanols and halogenated inhaled anesthetics such as halothane and isoflurane inhibit the archetypical voltage-gated Kv3 channel homolog K-Shaw2 by stabilizing the resting/closed states. By contrast, sevoflurane, a more heavily fluorinated ether commonly used in general anesthesia, specifically activates K-Shaw2 currents at relevant concentrations (0.05-1 mM) in a rapid and reversible manner. The concentration dependence of this modulation is consistent with the presence of high and low affinity interactions (K(D) = 0.06 and 4 mM, respectively). Sevoflurane (<1 mM) induces a negative shift in the conductance-voltage relation and increases the maximum conductance. Furthermore, suggesting possible roles in general anesthesia, mammalian Kv1.2 and Kv1.5 channels display similar changes. Quantitative description of the observations by an economical allosteric model indicates that sevoflurane binding favors activation gating and eliminates an unstable inactivated state outside the activation pathway. This study casts light on the mechanism of the novel sevoflurane-dependent activation of Kv channels, which helps explain how closely related inhaled anesthetics achieve specific actions and suggests strategies to develop novel Kv channel activators.