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Resveratrol, a phenolic substance present in grapes and a variety of medical plants, has been reported to induce vasorelaxation, however the mechanisms are uncertain. In this paper we investigate the possible participation of K+ channels in the endothelium-independent vasodilatation of rat aorta induced by resveratrol. Resveratrol induced concentration-dependent relaxation of rings with endothelium and without endothelium. We used different potassium channel inhibitors to determine whether the K+ channels mediated endothelium-independent relaxation of rat aorta induced by resveratrol. Highly selective blocker of ATP-sensitive K+ channels, glibenclamide, as well as non-selective blockers of K+ channels, tetraethylammonium, did not block resveratrol-induced relaxation of rat aortic rings. Charybdotoxin, a blocker of calcium-sensitive K+ channels did not affect the resveratrol-induced relaxation. 4-Aminopiridine, non-selective blocker of voltage-gated K+ (Kv) channels, and margatoxin that inhibits Kv1 channels abolished relaxation of rat aortic rings induced by resveratrol. In conclusion, we have shown that resveratrol potently relaxed rat aortic rings with denuded endothelium. It seems that 4-aminopiridine and margatoxin-sensitive K+ channels located in the smooth muscle of rat aorta mediated this relaxation. [ABSTRACT FROM AUTHOR]