Yamagishi T, Yanagisawa T, Satoh K, Taira N
Department of Pharmacology, Tohoku University School of Medicine, Sendai, Japan.
Eur J Pharmacol. 1994 Jan 14;251(2-3):253-62. doi: 10.1016/0014-2999(94)90407-3.
We investigated the relaxant mechanisms of the cyclic AMP (cAMP)-increasing agents, isoproterenol, T-0509, forskolin and 3-isobutyl-1-methylxanthine (IBMX), on porcine coronary arteries contracted with U46619 (300 nM), a thromboxane A2 analogue, or 30 mM KCl, by measuring force simultaneously with intracellular Ca2+ concentration ([Ca2+]i) or cAMP and cyclic GMP (cGMP) levels. In U46619-contracted arteries, these agents decreased [Ca2+]i and force of contraction to almost the same extent in a concentration-dependent manner, whereas in KCl-contracted arteries these agents, except IBMX at higher concentrations, produced a relaxation with little change in [Ca2+]i. These agents all elevated tissue cAMP levels, and in addition, IBMX at higher concentrations increased cGMP levels. In Ca(2+)-free medium, these agents produced a concentration-dependent inhibition of Ca2+ release from intracellular Ca2+ stores induced by U46619 but not by 25 mM caffeine. Isoproterenol at a high concentration (3 microM) transiently decreased [Ca2+]i but steadily relaxed KCl-contracted arteries. This decrease in [Ca2+]i, but not the relaxation was inhibited by ryanodine and caffeine treatments. These results suggest that the relaxant mechanism of these agents on KCl-contracted arteries is mainly due to phosphorylation of myosin light chain kinase via cAMP-dependent protein kinase, resulting in a reduction of the Ca2+ sensitivity of contractile elements. Their relaxant mechanism in U46619-contracted arteries seems due to the inhibition of signal transduction of the agonist, resulting in a decrease in [Ca2+]i and inhibition of the Ca2+ sensitization.
我们通过同时测量与细胞内钙离子浓度（[Ca2+]i）或环磷酸腺苷（cAMP）及环磷酸鸟苷（cGMP）水平相关的张力，研究了环磷酸腺苷（cAMP）升高剂异丙肾上腺素、T - 0509、福斯高林和3 - 异丁基 - 1 - 甲基黄嘌呤（IBMX）对用血栓素A2类似物U46619（300 nM）或30 mM氯化钾收缩的猪冠状动脉的舒张机制。在U46619收缩的动脉中，这些药物以浓度依赖的方式使[Ca2+]i和收缩力降低到几乎相同的程度，而在氯化钾收缩的动脉中，除高浓度的IBMX外，这些药物在[Ca2+]i几乎无变化的情况下产生舒张作用。这些药物均提高了组织cAMP水平，此外，高浓度的IBMX还增加了cGMP水平。在无钙培养基中，这些药物对U46619诱导的细胞内钙库钙离子释放产生浓度依赖性抑制，但对25 mM咖啡因诱导的钙离子释放无抑制作用。高浓度（3 microM）的异丙肾上腺素可短暂降低[Ca2+]i，但能持续舒张氯化钾收缩的动脉。这种[Ca2+]i的降低而非舒张作用受到兰尼碱和咖啡因处理的抑制。这些结果表明，这些药物对氯化钾收缩动脉的舒张机制主要是通过cAMP依赖性蛋白激酶使肌球蛋白轻链激酶磷酸化，导致收缩元件对钙离子的敏感性降低。它们在U46619收缩动脉中的舒张机制似乎是由于抑制了激动剂的信号转导，导致[Ca2+]i降低和钙离子致敏作用受到抑制。
