Effects of taurine on contractions of human internal mammary artery: a potassium channel opening action

OBJECTIVE: Taurine is an abun - dant amino acid that is widely distributed in hu - man and animal tissues. Pharmacodynamic studies show that taurine has hypotensive and myocardial protective effects. Studies in isolated tissue baths show that taurine relaxes precon - tracted arteries.This study aimed to show the ef - fects of taurine on human internal mammary artery (IMA) in vitro and to explain the mecha - nisms of its effects. METHODS: The response in the IMA was recorded isometrically by a force displacement transducer in isolated organ baths. Taurine (20, 40, 80 mM) was added to organ baths after pre - contraction with KCl (45 mM) or serotonin (5-HT, 30 µM). Taurine-induced relaxations were also tested in the presence of the cyclooxygenase in - hibitor indomethacin (10 µM), the nitric oxide synthase inhibitor L-NAME (100 µM), the large conductance Ca 2+ -activated K + channel inhibitor tetraethylammonium (TEA, 1 mM), the ATP-sen - sitive K + channel inhibitor glibenclamide (GLI, 10 µM), the voltage-sensitive K + channel inhibitor 4- aminopyridine (4-AP, 1 mM) and the inward recti - fier K + channel inhibitor barium chloride (BaCl 2, 30 µM). RESULTS: Taurine did not affect the resting tone of IMA. However, it produced relaxation in the 5-HT and KCl-precontracted preparations. The relaxation to IMA was not affected by GLI, 4- AP, BaCl 2, indomethacin and L-NAME. But, TEA inhibited taurine-induced relaxations significant - ly ( p < 0.05). CONCLUSIONS: The preincubation of IMA with taurine antagonized KCl and 5-HT induced con - tractions in a concentration dependent manner, while it did not affect the resting tone.The relax - ations to taurine were significantly antagonized by pretreatment withTEA. These results suggest that mechanism of va - sodilator effect of taurine in IMA may be the acti - vation of large conductance Ca 2+ -activated K +