Ginsenosides are major active ingredients of Panax ginseng. They have a number of pharmacological and physiological actions and are transformed into compound K (CK) or M4 by intestinal microorganisms. CK is derived from protopanaxadiol (PD) ginsenosides, whereas M4 is derived from protopanaxatriol (PT) ginsenosides. Recent reports show that ginsenosides act as pro-drugs for these metabolites. In previous work we demonstrated that the ginsenoside Rg2 regulates human 5-hydroxytryptamine3A (5-HT3A) receptor channel activity [Choi et al. (2003)]. In the present study, we investigated the effect of CK and M4 on the activity of the human 5-HT3A receptor channel. The 5-HT3A receptor was expressed in Xenopus oocytes, and the current was measured using the two-electrode voltage clamp technique. Treatment with CK or M4 had no effect on oocytes injected with 5-HT3A receptor cRNA. However pretreatment with M4 or CK followed by injection of 5-HT3A receptor cRNA led to reversible inhibition of the 5-HT-induced inward peak current (I5-HT). Half maximal inhibitory concentrations (IC50) of CK and M4 were 36.9

Keywords: 5-HT3A Receptor, CK and M4, Ginsenoside Metabolites, Ligand-gated Ion Channels, Panax Ginseng, Serotonin, Xenopus Oocytes