Goureau O, Tanfin Z, Harbon S
Endocrinologie et Régulations Cellulaires, CNRS URA 1131, Université Paris Sud, Orsay, France.
Biochem J. 1990 Nov 1;271(3):667-73. doi: 10.1042/bj2710667.
In pregnant-rat myometrium (day 21 of gestation), isoprenaline-induced cyclic AMP accumulation, resulting from receptor-mediated activation of adenylate cyclase, was negatively regulated by prostaglandins [PGE2, PGF2 alpha; EC50 (concn. giving 50% of maximal response) = 2 nM] and by the muscarinic agonist carbachol (EC50 = 2 microM). PG-induced inhibition was prevented by pertussis-toxin treatment, supporting the idea that it was mediated by the inhibitory G-protein Gi through the inhibitory pathway of the adenylate cyclase. Both isoprenaline-induced stimulation and PG-evoked inhibition of cyclic AMP were insensitive to Ca2+ depletion. By contrast, carbachol-evoked attenuation of cyclic AMP accumulation was dependent on Ca2+ and was insensitive to pertussis toxin. The inhibitory effect of carbachol was mimicked by ionomycin. Indirect evidence was thus provided for the enhancement of cyclic AMP degradation by a Ca2(+)-dependent phosphodiesterase activity in the muscarinic-mediated effect. The attenuation of cyclic AMP elicited by carbachol coincided with carbachol-stimulated inositol phosphate (InsP3, InsP2 and InsP) generation, which displayed an almost identical EC50 (3 microM) and was similarly unaffected by pertussis toxin. Both carbachol effects were reproduced by oxotremorine, whereas pilocarpine (a partial muscarinic agonist) failed to induce any decrease in cyclic AMP accumulation and concurrently was unable to stimulate the generation of inositol phosphates. These data support our proposal for a carbachol-mediated enhancement of a Ca2(+)-dependent phosphodiesterase activity, compatible with the rises in Ca2+ associated with muscarinic-induced increased generation of inositol phosphates. They further illustrate that a cross-talk between the two major transmembrane signalling systems contributed to an ultimate decrease in cyclic AMP in the pregnant-rat myometrium near term.
在妊娠大鼠子宫肌层（妊娠第21天）中，由受体介导的腺苷酸环化酶激活所导致的异丙肾上腺素诱导的环磷酸腺苷（cAMP）积累，受到前列腺素[前列腺素E2、前列腺素F2α；半数有效浓度（产生最大反应50%时的浓度）=2 nM]和毒蕈碱激动剂卡巴胆碱（半数有效浓度=2 μM）的负调控。百日咳毒素处理可阻止前列腺素诱导的抑制作用，这支持了该抑制作用是由抑制性G蛋白Gi通过腺苷酸环化酶的抑制途径介导的观点。异丙肾上腺素诱导的刺激以及前列腺素引起的环磷酸腺苷抑制对钙离子耗竭均不敏感。相比之下，卡巴胆碱引起的环磷酸腺苷积累减弱依赖于钙离子，且对百日咳毒素不敏感。离子霉素可模拟卡巴胆碱的抑制作用。因此，间接证据表明在毒蕈碱介导的效应中，钙离子依赖性磷酸二酯酶活性增强导致环磷酸腺苷降解增加。卡巴胆碱引起的环磷酸腺苷减弱与卡巴胆碱刺激的肌醇磷酸（肌醇三磷酸、肌醇二磷酸和肌醇一磷酸）生成同时出现，后者显示出几乎相同的半数有效浓度（3 μM），且同样不受百日咳毒素影响。氧化震颤素可重现卡巴胆碱的两种效应，而毛果芸香碱（一种部分毒蕈碱激动剂）未能诱导环磷酸腺苷积累的任何降低，同时也无法刺激肌醇磷酸的生成。这些数据支持了我们提出的卡巴胆碱介导钙离子依赖性磷酸二酯酶活性增强的观点，这与毒蕈碱诱导的肌醇磷酸生成增加所伴随的钙离子升高相一致。它们进一步说明，两个主要跨膜信号系统之间的相互作用导致了妊娠晚期大鼠子宫肌层中环磷酸腺苷的最终减少。
