Effects of ginsenosides on GABAA receptor channels expressed in xenopus oocytes
Ginsenosides, major active ingredients ofPanax ginseng, are known to regulate excitatory ligand-gated ion channel activity such as nicotinic acetylcholine and NMDA receptor channel activity. However, it is not known whether ginsenosides affect inhibitory ligand-gated ion channel activity. We investigated the effect of ginsenosides on human recombinant GABAA receptor (α1β1γ2S) channel activity expressed inXenopus oocytes using a two-electrode voltage-clamp technique. Among the eight individual ginsenosides examined, namely, Rb1, Rb2, Rc, Rd, Re, Rf, Rg1 and Rg2, we found that Rc most potently enhanced the GABA-induced inward peak current (l GABA). Ginsenoside Rc alone induced an inward membrane current in certain batches of oocytes expressing the GABAA receptor. The effect of ginsenoside Rc onI GABA was both dose-dependent and reversible. The half-stimulatory concentration (EC50) of ginsenoside Rc was 53.2 ± 12.3 μM. Both bicuculline, a GABAA receptor antagonist, and picrotoxin, a GABAA channel blocker, blocked the stimulatory effect of ginsenoside Rc onI GABA. Niflumic acid (NFA) and 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), both Cl− channel blockers, attenuated the effect of ginsenoside Rc onI GABA. This study suggests that ginsenosides regulated GABAA receptor expressed inXenopus oocytes and implies that this regulation might be one of the pharmacological actions ofPanax ginseng.
Key wordsPanax ginseng Ginsenosides GABA GABAA receptor Ligand-gated ion channels Xenopus oocytes
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