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KMID : 0370019980120000037
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Chung-Ang Journal of Pharmacal Sciences
1998 Volume.12 No. 0 p.37 ~ p.43
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Actions of Cyclic Nucleotides Associated with Receptive Relaxation in Stomach Smooth Muscle
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Abstract
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To investigate the actions of cyclic nucleotides associated with receptive relaxation, smooth muscle strips isolated from cat stomach were used to measure the isometric contraction in an isolated organ bath. Both sodium nitroprusside and forskolin inhibited acetylcholine-induced contraction dose-dependently. The inhibitory effect of sodium nitroprusside was more potent than that of forskolin. Verapamil, voltage-dependent calcium channel blocker, and TMB-8, a blocker of intracellular Ca^2+ release, significantly inhibited acetylcholine-induced contraction. Combined effects of verapamil and TMB-8 with sodium nitroprusside (0.1 μM) were significantly greater than that of each one, whereas those with forskolin (1 μM) were similar to that of each one. Tyrosine phosphatase inhibitor, vanadate (10 μM) significantly blocked the inhibitory effects of verapamil (1 μM), TMB -8 (1 μM) and forskolin (1 μM), but did not that of sodium nitroprusside (0.1 μM). However, protein kinase C activator, PMA (10 μM), did not affect the inhibitory effects of the above four agents. From the above results, it is suggested that the action of cAMP on receptive relaxation may be different from that of cGMP, which is modulated by tyrosine phosphatase in gastric smooth muscle.
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