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


METHODS
The effects of hinokiol on Na(+) channels were examined using the voltage-clamp (whole-cell mode) technique.


RESULTS
VGSC was blocked by hinokiol in a concentration-dependent and state-dependent manner in neuroblastoma N2A cells: IC(50) are 11.3 and 37.4μM 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.


CONCLUSIONS
Our results therefore suggest hinokiol inhibited VGSC in a closed-channel block manner and such inhibition involved intensification of channel inactivation.
Department of Chinese Pharmaceutical Sciences and Chinese Medicine Resources, China Medical University, Taichung, Taiwan.
Yu-Wen
YW
Wang
School of Chinese Medicine, China Medical University, Taichung, Taiwan.
Chin-Tsang
CT
Yang
Department of Physiology, China Medical University, Taichung, Taiwan.
Chi-Li
CL
Gong
Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan.
Yi-Hung
YH
Chen
Department of Physical Therapy, China Medical University, Taichung, Taiwan.
Yu-Wen
YW
Chen
Department of Anesthesiology, Eda-Hospital, I-Shou University, Kaohsiung, Taiwan.
King-Chuen
KC
Wu
Department of Biochemistry, China Medical University, Taichung, Taiwan.
Tzu-Hurng
TH
Cheng
Department of Chinese Pharmaceutical Sciences and Chinese Medicine Resources, China Medical University, Taichung, Taiwan; Department of Biotechnology, Asia University, Taichung, Taiwan.
Yueh-Hsiung
YH
Kuo
Department of Pharmacology, China Medical University, Taichung, Taiwan.
Yuh-Fung
YF
Chen
Department of Physiology, China Medical University, Taichung, Taiwan. Electronic address: ymleung@mail.cmu.edu.tw.
Yuk-Man
YM
Leung
D045784:Abietanes / Q000494:pharmacology*; D000818:Animals; D056547:CA1 Region, Hippocampal / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D061567:Voltage-Gated Sodium Channel Blockers / Q000494:pharmacology*; D061566:Voltage-Gated Sodium Channels / Q000378:metabolism*
D045784:Abietanes; D061567:Voltage-Gated Sodium Channel Blockers; D061566:Voltage-Gated Sodium Channels; C000610513:hinokiol
Block; Hinokiol; N2A cells; Rat hippocampal CA1 neurons; Voltage-gated Na(+) channels