Characterization of muscarinic receptor subtype mediating contraction and relaxation in equine coronary artery in vitro |
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Authors: | T OBI A KABEYAMA A NISHIO |
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Institution: | Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, Korimoto 1–21-24, Kagoshima 890, Japan;Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, Kagoshima 890, Japan |
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Abstract: | In coronary arterial rings isolated from horses, 10--8-10-6 mol/l acetylcholine (ACh) induced concentration-dependent contractions which were potentiated by the removal of endothelium and by pretreatment with I,-nitro-arginine (LNAG) or methylene blue (MB). Relatively lower concentrations of Ach 10-14-10-8 mol/l) induced relaxation when the coronary rings were contracted by phenylephrine (PE). ACh-induced contractions in the coronary rings without endothelium were competitively inhibited by each muscarinic subtype selective antagonist in the following order of potency: 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) > pirenzepine ≥ parafluoro-hexahydrosiladiphenidol (pFHHSiD) > methoctramine. ACh-induced relaxation in the rings with endothelium was inhibited by LNAG or MB, and by each selective antagonist in the following order of potency: 4-DAMP < pFHHSiD ≥ pirenzepine ≥ methoctramine. These results suggest that the ACh-induced contraction and relaxation in equine coronary arteries are mediated mainly by an M3-receptor located on the smooth muscle cells and endothelial cells, respectively, and that the stimulation of the M3-receptor on the endothelial cells liberates nitric oxide. |
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