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High-affinity blockade of voltage-operated skeletal muscle sodium channels by 2,6-dimethyl-4-chlorophenol

Published online by Cambridge University Press:  24 January 2006

G. Haeseler ,
S. Gudehus ,
J. Bufler ,
R. Dengler  and
M. Leuwer
G. Haeseler
Affiliation:
Hannover Medical School, Department of Anaesthesiology, Hannover, Germany
S. Gudehus
Affiliation:
Hannover Medical School, Department of Anaesthesiology, Hannover, Germany
J. Bufler
Affiliation:
Hannover Medical School, Department of Neurology and Clinical Neurophysiology, Hannover, Germany
R. Dengler
Affiliation:
Hannover Medical School, Department of Neurology and Clinical Neurophysiology, Hannover, Germany
M. Leuwer
Affiliation:
The University of Liverpool, University Department of Anaesthesia, Liverpool, UK
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Summary

Background and objective: The aromatic alcohol most closely resembling the aromatic tail of lidocaine is 2,6-dimethylphenol. This agent is as potent as lidocaine in blocking voltage-operated sodium channels. The aim of this study was to show the effect of halogenation in the para-position on the potency of this compound to block voltage-operated sodium channels. Methods: Insertion of the halogen chloride into the para-position of the molecule 2,6-dimethylphenol yielded 2,6-dimethyl-4-chlorophenol. Block of sodium currents by this compound was studied using heterologously expressed voltage-operated rat neuronal (rat IIa) sodium channels. Results: 2,6-dimethyl-4-chlorophenol reversibly suppressed depolarization-induced whole-cell sodium inward currents. The ECR50 for block of resting channels at a hyperpolarized holding potential (−150 mV) was 127 μmol, the Hill coefficient nH 1.7. Membrane depolarization inducing either fast or slow-inactivation strongly increased the blocking potency. This is an important feature of a local-anaesthetic-like action. The estimated half-maximum effect concentration for the fast-inactivated channel state ECI50 was 28 μmol, the Hill coefficient nH 3.8. When 20–30% of channels were slow-inactivated using long (2.5 s) prepulses, followed by a 10 ms repolarization period to allow recovery from fast inactivation, the IC50 at −100 mV holding potential was reduced to 53 μmol. Conclusion: These results, which show that 2,6-dimethyl-4-chlorophenol blocks voltage-operated sodium channels in a lidocaine-like manner while having a several fold higher potency than the non-halogenated parent compound, highlight a potentially meaningful principle of increasing the sodium channel blocking potency of phenol derivatives.

Keywords

SODIUM CHANNELS, voltage operatedANAESTHETICS LOCAL, phenol derivatives, lidocaineRATS
Type
Original Article
Information
European Journal of Anaesthesiology , Volume 23 , Issue 3 , March 2006 , pp. 190 - 196
Copyright
© 2006 European Society of Anaesthesiology

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