Eugenol inhibits sodium currents in dental afferent neurons.

Abstract

Although eugenol is widely used in dentistry, little is known about the molecular mechanisms responsible for its anesthetic properties. In addition to calcium channels, recently demonstrated by our group, there could be another molecular target for eugenol. Using a whole-cell patch-clamp technique, we investigated the effect of eugenol on voltage-gated sodium channel currents (I^sub Na^) in rat dental primary afferent neurons identified by retrograde labeling with a fluorescent dye in maxillary molars. Eugenol inhibited action potentials and I^sub Na^ in both capsaicin-sensitive and capsaicin-insensitive neurons. The pre-treatment with capsazepine, a competitive antagonist of transient receptor potential vanilloid 1 (TRPV1), failed to block the inhibitory effect of eugenol on I^sub Na^, suggesting no involvement of TRPV1. Two types of I^sub Na^, tetrodotoxin (TTX)-resistant and TTX-sensitive I^sub Na^, were inhibited by eugenol. Our results demonstrated that eugenol inhibits I^sub Na^ in a TRPV1-independent manner. We suggest that I^sub Na^ inhibition by eugenol contributes to its analgesic effect.