Inhibition of voltage-gated Na+ channels by hinokiol in neuronal cells

BackgroundHinokiol is a naturally occurring diterpenoid compound isolated from plants such as Taiwania cryptomerioides. Anti-oxidation, anti-cancer, and anti-inflammation effects of this compound have been reported. It is not yet known if hinokiol affects neurons or neuronal ion channel activities. We reported here that hinokiol inhibited voltage-gated Na+ channels (VGSC) in neuronal cells and we characterized the mechanisms of block.MethodsThe effects of hinokiol on Na+ channels were examined using the voltage-clamp (whole-cell mode) technique.ResultsVGSC was blocked by hinokiol in a concentration-dependent and state-dependent manner in neuroblastoma N2A cells: IC50 are 11.3 and 37.4 μM in holding potentials of −70 and −100 mV, respectively. In the presence of hinokiol there was a 13-mV left shift in steady-state inactivation curves; however, activation gating was not altered. VGSC inhibition by hinokiol did not require channel opening and was thus considered to be closed-channel block. In the presence of hinokiol, since the degree of block did not enhance with stimulation frequency, block by hinokiol thus did not exhibit use-dependence. Recovery from channel inactivation was not significantly affected in the presence of hinokiol. In addition, hinokiol also inhibited VGSC of differentiated neuronal NG108-15 cells and rat hippocampal CA1 neurons.ConclusionOur results therefore suggest hinokiol inhibited VGSC in a closed-channel block manner and such inhibition involved intensification of channel inactivation.