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


CONCLUSIONS
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.
Haeseler
G
G
Department of Anaesthesiology, Hannover Medical School, Hannover, Germany. Haeseler.Gertrud@MH-Hannover.de
Gudehus
S
S
Bufler
J
J
Dengler
R
R
Leuwer
M
M
D000465:Algorithms; D018686:Anesthetics, Intravenous / Q000378:metabolism / Q000494:pharmacology*; D002460:Cell Line; D004594:Electrophysiology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015742:Propofol / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014992:Xylenes / Q000494:pharmacology*
C514287:2,6-dimethyl-4-chlorophenol; D018686:Anesthetics, Intravenous; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D014992:Xylenes; D015742:Propofol