Taurine relaxes human radial artery through potassium channel opening action

The vascular actions and mechanisms of taurine were investigated in the isolated human radial artery (RA). RA rings were suspended in isolated organ baths and tension was recorded isometrically. First, a precontraction was achieved by adding potassium chloride (KCl, 45 mM) or serotonin (5-hydroxytryptamine, 5-HT, $30{\mu}M$) to organ baths. When the precontractions were stable, taurine (20, 40, 80 mM) was added cumulatively. Antagonistic effect of taurine on calcium chloride ($10{\mu}M$ to 10 mM) -induced contractions was investigated. Taurine-induced relaxations were also tested in the presence of the $K^+$ channel inhibitors tetraethylammonium (1 mM), glibenclamide ($10{\mu}M$) and 4-aminopyridine (1 mM). Taurine did not affect the basal tone but inhibited the contraction induced by 5-HT and KCl. Calcium chloride-induced contractions were significantly inhibited in the presence of taurine (20, 40, 80 mM) (p<0.05). The relaxation to taurine was inhibited by tetraethylammonium (p<0.05). However, glibenclamide and 4-aminopyridine did not affect taurine -induced relaxations. Present experiments show that taurine inhibits 5-HT and KCl -induced contractions in RA, and suggest that large conductance $Ca^{2+}$-activated $K^+$ channels may be involved in taurine -induced relaxation of RA.