Quercetin Inhibits α3β4 Nicotinic Acetylcholine Receptor-Mediated Ion Currents Expressed in Xenopus Oocytes

Quercetin mainly exists in the skin of colored fruits and vegetables as one of flavonoids. Recent studies show that quercetin, like other flavonoids, has diverse pharmacological actions. However, relatively little is known about quercetin effects in the regulations of ligand-gated ion channels. In the previous reports, we have shown that quercetin regulates subsets of homomeric ligand-gated ion channels such as glycine, 5-HT(3A) and α7 nicotinic acetylcholine receptors. In the present study, we examined quercetin effects on heteromeric neuronal α3β4 nicotinic acetylcholine receptor channel activity expressed in Xenopus oocytes after injection of cRNA encoding bovine neuronal α3 and β4 subunits. Treatment with acetylcholine elicited an inward peak current (I(ACh)) in oocytes expressing α3β4 nicotinic acetylcholine receptor. Co-treatment with quercetin and acetylcholine inhibited I(ACh) in oocytes expressing α3β4 nicotinic acetylcholine receptors. The inhibition of I(ACh) by quercetin was reversible and concentration-dependent. The half-inhibitory concentration (IC(50)) of quercetin was 14.9±0.8 µM in oocytes expressing α3β4 nicotinic acetylcholine receptor. The inhibition of I(ACh) by quercetin was voltage-independent and non-competitive. These results indicate that quercetin might regulate α3β4 nicotinic acetylcholine receptor and this regulation might be one of the pharmacological actions of quercetin in nervous systems.