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Abstract

Ginsenosides, major active ingredients of Panax ginseng, are known to regulate the excitatory ligandgated ion channel activity. Recent reports showed that ginsenosides attenuate nicotinic acetylcholine and NMDA receptor channel activity. However, it is not known whether ginsenosides also affect the inhibitory ligand-gated ion channel activity. We investigated the effect of ginsenosides on human glycine alpha1 receptor channel activity expressed in Xenopus oocytes using a two- electrode voltage clamp technique. Treatment of ginsenoside Rf enhances glycine-induced inward peak current (I-Gly) with dose dependent and reversible manner but ginsenoside Rf itself did not elicit membrane currents. The half-stimulatory concentrations (EC50) of ginsenoside Rf was 49.8 +/- 8.9 muM. Glycine receptor antagonist strychnine completely blocked the inward current elicited by glycine plus ginsenoside RE Cl- channel blocker 4,4'-disothiocyanostilbene-2,2'-disulfonic acid (DIDS) also blocked the inward current elicited by glycine plus ginsenoside RE We also tested the effect of eight individual ginsenosides (i.e., Rb-1, Rb-2, Re, Rd, Re, Rg(1), Rg(2), and Ro) in addition to ginsenoside RE We found that five of them significantly enhanced the inward current induced by glycine with the following order of potency: Rb-1 > Rb-2 > Rg(2) greater than or equal to Rc > Rf > Rg(1) > Re. These results indicate that ginsenosides might regulate gylcine receptor expressed in Xenopus oocytes and this regulation might be one of the pharmacological actions of Panax ginseng.