Cardio-Electopharmacology and Vasodilating Mechanisms of Quercetin

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Quercetin, a kind of flavonoids, exerts the cardiovascular actions. In guinea pig ventricular cardiomyocytes, quercetin depresses the action potential duration (APD) and inhibited the underlying ionic currents ICaL.,IKrec. IK1 in cardiomyocytes. In rat aorta, quercetin (0.1 to 100 μM) relaxed the contraction induced by pretreatment with 5 μM norepinephrine (NE) in aconcentration-dependent manner. NG-monomethyl-L-arginine acetate (L-NMMA) at 100 μM reduced the quercetin (100 μM)-induced vasorelaxation from 97.0 ± 3.7% (n=10, p<0.05) to 78.0 ± 11.6% (n=5, p<0.05). Endothelium removal as well attenuated the vasodilatation. In the presence of both 100 μM L-NMMA and 10 μM indomethacin, the quercetin-induced vasorelaxation was further attenuated by high K (30 mM) or 10 μM tetraethylammonium (TEA). Among KCa channel inhibitors, the quercetin-induced vasodilatation was attenuated by 0.3 μM apamin (sensitive to SK), but not by 30 nM charybdotoxin (sensitive to BK and IK). Under KCl-induced vasoconstriction, the quercetin-induced vasorelaxation was attenuated by PK-C inhibitors; Go6983 (α-, β-, γ-, δ and ζ-sensitive) produced stronger than Ro-31-8425 (α-, β-, γ- and e-sensitive). In rat mesenteric artery, the quercetininduced vasodilatation was almost resistant to both 100 μM L-NG-nitro arginine methyl ester (L-NAME) and 100 μM indomethacin. The L-NAME/indomethacin-resistant quercetin-induced was not modified by TEA (1 mM), but was attenuated by endothelium removal and 100 μM 18α- and 50 μM 18β-glychrrhetinic acids (gap junction inhibitors). Therefore, quercetin dilates the vascular smooth muscle mediated by endothelium-dependent and -independent mechanisms.