Methyl syringate, a low-molecular-weight phenolic ester, as an activator of the chemosensory ion channel TRPA1

Transient receptor potential channel ankryn 1 (TRPA1) and transient receptor potential channel vanilloid 1 (TRPV1) are members of the TRP superfamily of structurally related, nonselective cation channels and are often coexpressed in sensory neurons. Extracts of the first leaves of Kalopanax pictus Nakai (Araliaceae) have been shown to activate hTRPA1 and hTRPV1. Therefore, the effects of six commercially available chemicals (methyl syringate, coniferyl alcohol, protocatechuic acid, hederacoside C, alpha-hederin, and eleutheroside B) found in K. pictus were investigated on cultured cells expressing hTRPA1 and hTRPV1. Of the six compounds, methyl syringate selectively activated hTRPA1 (EC50 = 507.4 mu M), but not hTRPV1. Although methyl syringate had a higher EC50 compared with allyl isothiocyanate (EC50 = 7.4 mu M) and cinnamaldehyde (EC50 = 22.2 mu M), the present study provides evidence that methyl syringate from K. pictus is a specific and selective activator of hTRPA1.