Kubalak S W, Newman W H, Webb J G
Department of Cell and Molecular Pharmacology, Medical University of South Carolina, Charleston 29425.
J Mol Cell Cardiol. 1991 Feb;23(2):199-205. doi: 10.1016/0022-2828(91)90106-v.
Cyclic AMP regulation by muscarinic and adenosine receptors was investigated in isolated canine ventricular myocytes. Both the muscarinic receptor agonist, carbachol, and the adenosine receptor agonist, phenylisopropyladenosine, decreased isoproterenol-stimulated cyclic AMP accumulation in a concentration-dependent manner. Carbachol was more potent than phenylisopropyladenosine and had a greater inhibitory effect. At 10(-6) M, carbachol reduced isoproterenol-stimulated cyclic AMP by 73 +/- 5% while 10(-3) M phenylisopropyladenosine was required to decrease cyclic AMP accumulation by 54 +/- 8%. Pretreatment of myocytes with pertussis toxin to inactivate the inhibitory guanine nucleotide binding protein, Gi, completely abolished the effect of phenylisopropyladenosine to reduce cyclic AMP stimulation. In comparison, pertussis toxin treatment blunted the response to carbachol and shifted the dose-effect curve to the right but did not eliminate the inhibitory action of carbachol. In toxin-treated myocytes, 10(-3) M carbachol produced a 26 +/- 6% reduction of isoproterenol-induced cyclic AMP accumulation. This pertussis toxin-insensitive action of carbachol was antagonized by atropine and pirenzepine and was prevented when either of two different phosphodiesterase inhibitors. RO-20-1724 or isobutylmethylxanthine, was included in the incubation medium. The results indicate that adenosine receptor-mediated inhibition of hormone-stimulated cyclic AMP accumulation in ventricular myocytes occurs by a single, Gi-dependent mechanism while muscarinic inhibition appears to involve both Gi-dependent and Gi-independent mechanisms. The Gi-independent mechanism may reflect enhanced phosphodiesterase activity which results from the activation of muscarinic receptors.
在分离的犬心室肌细胞中研究了毒蕈碱受体和腺苷受体对环磷酸腺苷（cAMP）的调节作用。毒蕈碱受体激动剂卡巴胆碱和腺苷受体激动剂苯异丙基腺苷均以浓度依赖的方式降低异丙肾上腺素刺激的cAMP积累。卡巴胆碱比苯异丙基腺苷更有效，且具有更强的抑制作用。在10⁻⁶ M时，卡巴胆碱使异丙肾上腺素刺激的cAMP降低73±5%，而需要10⁻³ M苯异丙基腺苷才能使cAMP积累降低54±8%。用百日咳毒素预处理心肌细胞以灭活抑制性鸟嘌呤核苷酸结合蛋白Gi，完全消除了苯异丙基腺苷降低cAMP刺激的作用。相比之下，百日咳毒素处理减弱了对卡巴胆碱的反应，并使剂量效应曲线右移，但并未消除卡巴胆碱的抑制作用。在毒素处理的心肌细胞中，10⁻³ M卡巴胆碱使异丙肾上腺素诱导的cAMP积累降低26±6%。卡巴胆碱这种对百日咳毒素不敏感的作用被阿托品和哌仑西平拮抗，并且当两种不同的磷酸二酯酶抑制剂RO - 20 - 1724或异丁基甲基黄嘌呤中的任何一种包含在孵育培养基中时可被阻止。结果表明，腺苷受体介导的心室肌细胞中激素刺激的cAMP积累的抑制作用通过单一的、依赖Gi的机制发生，而毒蕈碱抑制似乎涉及依赖Gi和不依赖Gi的机制。不依赖Gi的机制可能反映了毒蕈碱受体激活导致的磷酸二酯酶活性增强。
