Eugenol Inhibits Calcium Currents in Dental Afferent Neurons

Eugenol is a topical analgesic agent widely used in the dental clinic. To elucidate the molecular mechanism underlying its analgesic action, we investigated the effect of eugenol on high-voltage-activated calcium channel (HVACC) currents in dental primary afferent neurons, and with a heterologous expression system. Dental primary afferent neurons were identified by retrograde labeling with a fluorescent dye, DiI. Eugenol inhibited HVACC currents in both capsaicin-sensitive and capsaicin-insensitive dental primary afferent neurons. The HVACC inhibition by eugenol was not blocked by capsazepine, a competitive transient receptor potential vanilloid 1 (TRPV1) antagonist. Eugenol inhibited N-type calcium currents in the cell line C2D7, stably expressing the human N-type calcium channels, where TRPV1 was not endogenously expressed. Our results suggest that the HVACC inhibition by eugenol in dental primary afferent neurons, which is not mediated by TRPV1 activation, might contribute to eugenol’s analgesic effect. Abbreviations: high-voltage-activated calcium channel, HVACC; transient receptor potential vanilloid 1, TRPV1; trigeminal ganglion, TG; dorsal root ganglion, DRG; capsazepine, CZP.