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 α3β4, α7 or human muscle αβδε subunits. Treatment with acetylcholine elicited an inward peak current (I_ACh) in oocytes expressing nicotinic acetylcholine receptor subtypes. Cotreatment with ginsenoside Rg₂ and acetylcholine inhibited I_ACh in oocytes expressing with α3β4 or αβδε but not in oocytes expressing α7 nicotinic acetylcholine receptors. The inhibition of I_ACh by ginsenoside Rg₂ was reversible and dose-dependent. The half-inhibitory concentrations (IC₅₀) of ginsenoside Rg₂ were 60.2±14.1 and 15.7±3.5 μM in oocytes expressing α3β4 and αβδε nicotinic acetylcholine receptors, respectively. The inhibition of I_ACh by ginsenoside Rg₂ was voltage-independent and noncompetitive. Other ginsenosides besides ginsenoside Rg₂ also inhibited I_ACh in oocytes expressing α3β4 or αβδε nicotinic acetylcholine receptors. The order of potency for the inhibition of I_ACh was ginsenoside Rg₂>Rf>Re>Rg₁>Rc>Rb₂>Rb ₁ in oocytes expressing α3β4 nicotinic acetylcholine receptors and was ginsenoside Rg₂>Rf>Rg₁>Re>Rb₁>Rc>Rb ₂ in oocytes expressing αβδε nicotinic acetylcholine receptors. These results indicate that ginsenosides might regulate nicotinic acetylcholine receptors in a differential manner and this regulation might be one of the pharmacological actions of Panax ginseng.