Pore opening, not voltage sensor movement, underpins the voltage-dependence of facilitation by a hERG blocker.

Ryotaro Kawano, Furutani Kazuharu, Ichiwara Minami, Adachi Ryo, Clancy Colleen, Sack Jon, Kita Satomi

doi:10.1124/molpharm.122.000569

<p>A drug that blocks the cardiac myocyte voltage-gated K⁺ channels encoded by the hERG carries a potential risk of long QT syndrome and life-threatening cardiac arrhythmia. Interestingly, certain hERG blockers can also facilitate hERG activation to increase hERG currents, which may reduce proarrhythmic potential. However, the molecular mechanism remains unclear. The hallmark feature of the facilitation effect by hERG blockers is that a depolarizing preconditioning pulse shifts voltage-dependence of hERG activation to more negative voltages. Here we utilize a D540K hERG mutant to study the mechanism of the facilitation effect. D540K hERG is activated by not only depolarization but also hyperpolarization. With D540K hERG, we find that nifekalant, a hERG blocker and Class III antiarrhythmic agent, blocks and facilitates not only current activation by depolarization but also current activation by hyperpolarization, suggesting a shared gating process upon depolarization and hyperpolarization. Moreover, in response to hyperpolarizing conditionings, nifekalant facilitates D540K hERG currents but not wild-type currents. Our results indicate that induction of facilitation is coupled to pore opening, not voltage per se. We propose that gated access to the hERG central cavity underlies the voltage-dependence of induction of facilitation.</p>

Pore opening, not voltage sensor movement, underpins the voltage-dependence of facilitation by a hERG blocker.

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