Depenedence of Ependence 6β-Acetoxyl-7α-Hydroxyroyleanone Block of Kv1.2 Channels on C-Type Inactivation

Abstract

Voltage-gated K+ (Kv) channels repolarize excitable cells by providing a pathway for K+ efflux. Kv channels activate when the membrane is depolarized, and subsequently exhibit slow inactivation (C-type inactivation) during continuous depolarization. A selective pharmacological agent targeting C-type inactivation is so far lacking. Here we reported that 6β-acetoxy-7α-hydroxyroyleanone (AHR), a diterpenoid compound isolated from Taiwania cryptomerioides Hayata, could selectively modify C-type inactivation of Kv1.2 channels. Extracellular, but not intracellular, AHR (50 μM) dramatically speeded up the slow decay of Kv currents and left-shifted the steady-state inactivation curve. AHR blocked steady-state Kv currents with an IC50 of 17.7 μM and the effects of AHR were completely reversible. AHR did not affect at all the kinetics and voltage-dependence of Kv1.2 channel activation. The degree of block of Kv currents by AHR was independent of the intracellular K+ concentration. In addition, effect of AHR was much attenuated in a Kv1.2 V370G mutant defective in C-type inactivation. Furthermore, ATP-sensitive K+ (KATP) channel, which does not display C-type inactivation, was not affected by AHR. Therefore, block of Kv1.2 channel by AHR did not appear to involve direct occlusion of the outer pore but may depend on the C-type inactivation gate. AHR could thus be a pharmacological tool targeting the C-type inactivation gate of Kv channels.