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Voltage-dependent block of neuronal and skeletal muscle sodium channels by thymol and menthol

Published online by Cambridge University Press:  16 August 2006

G. Haeseler
Affiliation:
Hannover Medical School, Department of Anaesthesiology, Hannover, Germany
D. Maue
Affiliation:
Hannover Medical School, Department of Anaesthesiology, Hannover, Germany
J. Grosskreutz
Affiliation:
Hannover Medical School, Department of Neurology and Neurophysiology, Hannover, Germany
J. Bufler
Affiliation:
Hannover Medical School, Department of Neurology and Neurophysiology, Hannover, Germany
B. Nentwig
Affiliation:
Hannover Medical School, Department of Anaesthesiology, Hannover, Germany
S. Piepenbrock
Affiliation:
Hannover Medical School, Department of Anaesthesiology, Hannover, Germany
R. Dengler
Affiliation:
Hannover Medical School, Department of Neurology and Neurophysiology, Hannover, Germany
M. Leuwer
Affiliation:
University of Liverpool, University Department of Anaesthesia, Liverpool, UK
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Abstract

Background and objective: Thymol is a naturally occurring phenol derivative used in anaesthetic practice as a stabilizer and preservative of halothane, usually at a concentration of 0.01%. Although analgesic effects have long been described for thymol and its structural homologue menthol, a molecular basis for these effects is still lacking. We studied the blocking effects of thymol and menthol on voltage-activated sodium currents in vitro as possible molecular target sites.

Methods: Whole cell sodium inward currents via heterologously (HEK293 cells) expressed rat neuronal (rat type IIA) and human skeletal muscle (hSkM1) sodium channels were recorded in the absence and presence of definite concentrations of either thymol or menthol.

Results: When depolarizing pulses to 0 mV were started from a holding potential of-70 mV, halfmaximum blocking concentrations (IC50) for the skeletal muscle and the neuronal sodium channel were 104 and 149 µmol for thymol and 376 and 571 µmol for menthol. The blocking potency of both compounds increased at depolarized holding potentials with the fraction of inactivated channels. The estimated dissociation constant K d for thymol and menthol from the inactivated state was 22 and 106 µmol for the neuronal and 23 and 97 µmol for the skeletal muscle sodium channel, respectively.

Conclusions: The results suggest that antinociceptive and local anaesthetic effects of thymol and menthol might be mediated via blockade of voltage-operated sodium channels with the phenol derivative thymol being as potent as the local anaesthetic lidocaine.

Type
Original Article
Copyright
2002 European Society of Anaesthesiology

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