Eugenol inhibits K+ currents in trigeminal ganglion neurons

Eugenol, a natural capsaicin congener, is widely used in dentistry. Eugenol inhibits voltage-activated Na + and Ca 2+ channels in a transient receptor potential vanilloid 1 (TRPV1)-independent manner. We hypothesized that eugenol also inhibits voltage-gated K + currents, and investigated this in rat trigeminal ganglion neurons and in a heterologous system using whole-cell patch clamping. Eugenol inhibited voltage-gated K + currents, and the inhibitory effects of eugenol were observed in both capsaicin-sensitive and capsaicin-insensitive neurons. Pre-treatment with capsazepine, a well-known antagonist of TRPV1, failed to block the inhibitory effects of eugenol on K + currents, suggesting no involvement of TRPV1. Eugenol inhibited human Kv1.5 currents stably expressed in Ltk - cells, where TRPV1 is not endogenously expressed. We conclude that eugenol inhibits voltage-gated K + currents in a TRPV1-independent manner. The inhibition of voltage-gated K + currents is likely to contribute to the irritable action of eugenol. Abbreviations: human Kv 1.5 channel, hKv1.5; transient receptor potential vanilloid 1, TRPV1.1