Ginsenosides, or ginseng saponins, are biologically active ingredients of Panax ginseng. Accumulating evidence suggests that ginsenosides can alleviate pain from injections of noxious chemicals, such as capsaicin [Nah et al. (2000)]. In this study we examined the ef-fects of ginsenoside Rc on the capsaicin-induced in-ward current in Xenopus oocytes that expresses the vanilloid receptor 1 (VR1). Ginsenoside Rc enhanced the capsaicin-induced inward current in a concentra-tion-dependent and reversible manner, but ginsenoside Rc itself elicited no membrane currents. The VR1 an-tagonist capsazepine almost completely blocked the inward current that was elicited by capsaicin plus gin-senoside Rc. We also tested the effect of seven other fractionated ginsenosides (i.e., Rb1, Rb2, Rd, Re, Rf, Rg1, and Rg2) in addition to ginsenoside Rc. We found that six of them significantly enhanced the inward current that is induced by capsaicin with the following order of potency: Rc > Rf > Rg1 ?Rd > Rb2 > Rb1. These results show the possibility that the in vivo effect of ginsenosides against capsaicin-induced pain is de-rived from their modulation of the VR1 channel func-tion.

Keywords: Ginsenosides, Vanilloid Receptor, Capsaicin, Pain