Effects of ginsenosides, active components of ginseng, on nicotinic acetylcholine receptors expressed in Xenopus oocytes

We investigated the effects of ginsenosides, the active ingredient of ginseng, on neuronal or muscle-type nicotinic acetylcholine receptor channel activity expressed in Xenopus oocytes after injection of cRNA encoding bovine neuronal alpha3beta4, alpha7 or human muscle abetadeltaepsilon subunits. Treatment with acetylcholine elicited an inward peak current (I-ACh) in oocytes expressing nicotinic acetylcholine receptor subtypes. Cotreatment with ginsenoside Rg(2) and acetylcholine inhibited I-ACt, in oocytes expressing with alpha3beta4 or cco6e but not in oocytes expressing alpha7 nicotinic acetylcholine receptors. The inhibition Of IACh by ginsenoside Rg(2), was reversible and dose-dependent. The half-inhibitory concentrations (IC50) of ginsenoside Rg(2) were 60.2 +/- 14.1 and 15.7 +/- 3.5 muM in oocy-tes expressing alpha3beta4 and alphabetadeltaepsilon nicotinic acetylcholine receptors, respectively. The inhibition of I-ACh by ginsenoside Rg(2) was voltage -independent and noncompetitive, Other ginsenosides besides ginsenoside Rg(2) also inhibited I-ACh, in oocytes expressing alpha3beta4 or alphabetadeltaepsilon nicotinic acetylcholine receptors. The order of potency for the inhibition of 1,c 1, was ginsenoside Rg(2) > Rf > Re > Rg(1) > Rc > Rb-2 > Rb-1 in oocytes expressing alpha3beta4 nicotinic acetylcholine receptors and was ginsenoside Rg(2) > Rf > Rg(1) > Re > Rb-1 > Rc> Rb-2 in oocytes expressing nicotinic acetylcholine receptors. These results indicate that ginsenoside, might regulate nicotinic acetylcholine receptors in a differential manner and this regulation might be one of the pharmacological actions of Panax ginseng. (C) 2002 Elsevier Science B.V. All rights reserved.