High-affinity blockade of voltage-operated skeletal muscle sodium channels by 2,6-dimethyl-4-chlorophenol.
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 micromol, 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 micromol, 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 micromol. 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.[1]References
- High-affinity blockade of voltage-operated skeletal muscle sodium channels by 2,6-dimethyl-4-chlorophenol. Haeseler, G., Gudehus, S., Bufler, J., Dengler, R., Leuwer, M. European journal of anaesthesiology. (2006) [Pubmed]
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