Fleming N, Sliwinski-Lis E, Burke D N
Faculty of Dentistry, Department of Oral Biology, University of Manitoba, Winnipeg, Canada.
Life Sci. 1989;44(15):1027-35. doi: 10.1016/0024-3205(89)90554-7.
The involvement of G regulatory proteins in muscarinic receptor signal transduction was examined in electrically permeabilized rat submandibular acinar cells. The guanine nucleotide analog, GTP gamma S, caused the dose dependent hydrolysis of membrane phosphatidylinositol 4,5-bisphosphate to release IP3. This response was insensitive to pertussis toxin treatment and was duplicated by NaF but not by GDP beta S. Enhanced IP3 synthesis was observed with a combination of GTP gamma S and carbachol. Exogenous IP3, as well as carbachol and GTP gamma S, provoked the release of sequestered 45Ca2+ from non-mitochondrial stores. In intact cells, carbachol significantly reduced the level of cyclic AMP induced by the beta-adrenergic agonist, isoproterenol, to 69% of its normal value. Pertussis toxin abolished this inhibitory action of carbachol on cyclic nucleotide levels. These results suggest that muscarinic receptors are coupled to two separate G regulatory proteins in submandibular mucous acini-the pertussis toxin-insensitive Gp of the phosphoinositide transduction pathway associated with elevated cytosolic calcium levels, and the pertussis toxin-sensitive Gi inhibitory protein of the adenylate cyclase complex.
在电通透的大鼠下颌下腺腺泡细胞中研究了G调节蛋白在毒蕈碱受体信号转导中的作用。鸟嘌呤核苷酸类似物GTPγS引起膜磷脂酰肌醇4,5-二磷酸的剂量依赖性水解以释放IP3。该反应对百日咳毒素处理不敏感，可被NaF重复，但不能被GDPβS重复。观察到GTPγS和卡巴胆碱联合使用可增强IP3合成。外源性IP3以及卡巴胆碱和GTPγS可促使非线粒体储存中螯合的45Ca2+释放。在完整细胞中，卡巴胆碱可将β-肾上腺素能激动剂异丙肾上腺素诱导的环磷酸腺苷水平显著降低至其正常值的69%。百日咳毒素消除了卡巴胆碱对环核苷酸水平的这种抑制作用。这些结果表明，毒蕈碱受体与下颌下黏液腺泡中的两种不同G调节蛋白偶联——与胞质钙水平升高相关的磷脂酰肌醇转导途径中对百日咳毒素不敏感的Gp，以及腺苷酸环化酶复合物中对百日咳毒素敏感的Gi抑制蛋白。
