Molecular mechanism of volatile anesthetic action on the cardiac IKs channel

Abstract

The cardiac slow delayed rectifier potassium current, IKs, is a major repolarizing current. The IKs channel consists of the pore-forming α-subunit (KCNQ1) and the auxiliary β-subunit (KCNE1). Among the cardiac ion channels, IKs is the most sensitive to inhibition by volatile anesthetics, but the underlying molecular mechanism is unknown. The goal of this study was to investigate the mechanism of volatile anesthetic action on this channel. The hypothesis that a volatile anesthetic, isoflurane, inhibited IKs by direct interaction with KCNQ1 α-subunit was tested. Whole-cell patch clamp experiments were carried out using HL-1 cells, a cardiac muscle cell line derived from the AT1 mouse atrial myocyte tumor lineage. Cells were transiently transfected with the genes encoding for KCNQ1, KCNE1, and an F340C KCNQ1 mutant. In the presence of a clinically relevant concentration of isoflurane (0.82 ± 0.01 mM), the IKs current (KCNQ1+KCNE1) was inhibited by 56.0±9.6% relative to control levels measured at a test pulse to +60 mV from a holding potential of −40 mV. In the absence of KCNE1, isoflurane inhibited KCNQ1 by 86.2±2.5%. The effect of isoflurane was significantly attenuated in the F340C mutant where the resultant current was inhibited by 23.2±0.7%. Our results show that isoflurane interacted with the F340 residue located on the KCNQ1 S6 domain. Furthermore, the KCNE1 β-subunit also modulated the isoflurane effect on IKs. Supported by NIH RO1 GM067675.