Figure 3. Inhibition of voltage-gated K⁺ currents by eugenol does not require TRPV1 activation. (A) Capsazepine (CZP) did not block the inhibition of voltage-gated K⁺ currents by eugenol in rat trigeminal ganglion (TG) neurons. The representative traces of voltage-gated K⁺ currents under control, CZP (10 µM), and the combined application of eugenol and CZP (left). The inhibition of voltage-gated K⁺ currents by the combined application of eugenol and CZP was not significantly different from that of eugenol only (mean ± SEM, p > 0.05) (right), indicating that eugenol-induced voltage-gated K⁺ current inhibition was TRPV1-independent. The number in parentheses represents the number of cells studied. (B) Representative current traces under control and 1 mM eugenol in Ltk^– cells (left). Eugenol inhibited hKv1.5 currents in Ltk^– cells. The summary of K⁺ current inhibition in trigeminal ganglion neurons and Ltk^– cells (right). The K⁺ current inhibition by eugenol in trigeminal ganglion neurons was significantly greater than that in Ltk^– cells (mean ± SEM, p < 0.05). (Insert) RT-PCR analysis shows no endogenous expression of TRPV1 in Ltk^– cells. TRPV1 is clearly expressed in trigeminal ganglion neurons. The expected sizes of PCR products were 233 bp (TRPV1) and 293 bp (β-actin). No PCR products were detected with H₂O (lane –).