Quercetin Activates Wild Type HKv1.5 Channel Expressed In Xenopus Oocytes By A Residue I502 In S6 Transmembrane Domain

Aim: The objectives of this study were to investigate the pharmacological effects of quercetin on wild-type (WT) and mutant (I502A) hkv1.5 channel currents (Ikur), and identified whether mutation in the S6 segment is critical to activation of Ikur by quercetin.Methods: Experiments were carried out on WT and site directed mutated hkv1.5 channels stably expressed in Xenopus oocytes using the two-electrode voltage-clamp technique.Results: Quercetin increased WT hkv1.5 channel currents in concentration, voltage and time-dependent manners, the EC50 was 37.8μmol/L, and the steady state activation and inactivation parameters was negatively shifed. Quercetin accelerated channel activation and inactivation, and the activation and inactivation time constants were also significantly decreased. However, mutating I502 residue to Ala abolished the activation effect of quercetin. The activation and inactivation kinetics, activation and inactivation time constants were not modified by quercetin for the I502A channel. As an antioxidant, tanshinone IIA inhibited H2O2-induced activation effect on WT hkv1.5, but quercetin showed a nonsignificant tendency on it. Conclusion: We conclude that 1) quercetin preferentially binds to and activates WT hKv1.5 channel, simultaneouly increases IKur amplitude; 2) Ile502,an aliphatic and neutral amino acid residue resided in the S6 segment, is important in the quercetin-binding site; 3) quercetin-induced changes in WT hkv1.5 properties may be foreign to itself anti-oxidative action.