Vasorelaxant effect of taurine is diminished by tetraethylammonium in rat isolated arteries

Although the vasorelaxant effects of taurine have been studied in rabbit ear artery, rat isolated aorta and mesenteric artery, its pharmacological properties in other vascular beds and underlying mechanism(s) are still not well clarified. The present study was designed to observe the effects of taurine on the contractions induced by depolarization and phenylephrine in rat isolated aortic, renal and mesenteric arterial rings, and to get an insight into its mechanism(s). Arterial rings were suspended in organ baths and tension was recorded isometrically. Taurine 20–80 mM produced concentration-dependent relaxations of rat isolated aortic rings precontracted by 30 mM potassium chloride and 1 μM phenylephrine; the maximal relaxation was 17.17 ± 3.18% and 22.23 ± 1.83% respectively. The relaxation was not affected by 0.1 mM NG-nitro-l-arginine methylester ester (a nitric oxide synthetase inhibitor), 10 μM indomethacin (a cyclooxygenase inhibitor), 1 mM 4-aminopyridine (a KV blocker), 10 μM glibenclamide (a KATP blocker), 1 mM barium chloride (BaCl2, a KIR blocker), and 100 nM iberiotoxin (a BKCa blocker), but was nearly abolished by 10 mM tetraethylammonium (TEA, a non-selective potassium channel blocker). Preincubation with taurine 20–60 mM did not affect the basal tone but inhibited the contraction induced by phenylephrine, and the inhibitory effect was attenuated by TEA in isolated renal and mesenteric arterial rings. Present experiments show that taurine relaxes contracted rat aorta and inhibits the phenylephrine-induced contraction of renal and mesenteric arteries, and suggest that a mechanism related to potassium channel opening may be involved in the action of taurine.