Merritt J E, Taylor C W, Rubin R P, Putney J W
Biochem J. 1986 Jun 1;236(2):337-43. doi: 10.1042/bj2360337.
The initial response of many cells to 'Ca2+-mobilizing' agonists is phospholipase C-mediated hydrolysis of phosphatidylinositol bisphosphate to inositol trisphosphate (IP3) and diacylglycerol. It has been suggested, by analogy with receptor regulation of adenylate cyclase, that 'Ca2+-mobilizing' receptors may interact with a guanine nucleotide-binding protein (G protein) to regulate phospholipase C activity. Here we report increased accumulation of IP3 in response to caerulein or carbachol in electrically permeabilized rat pancreatic acinar cells. The stable analogues of GTP (guanosine 5'-[gamma-thio]trisphosphate and guanosine 5'-[beta, gamma-imido]triphosphate) stimulate IP3 accumulation and potentiate the effects of caerulein and carbachol. This synergism demonstrates an interaction between receptors, a G protein and phospholipase C. These responses are unaffected by pretreatment of the cells with pertussis or cholera toxins under conditions that produce substantial covalent modification of Gi and Gs, the proteins that couple receptors to adenylate cyclase. We therefore conclude that the G protein that couples receptors to phospholipase C in exocrine pancreas is probably neither Gi nor Gs; instead, we propose that a different G protein mediates this effect.
许多细胞对“钙动员”激动剂的初始反应是磷脂酶C介导的磷脂酰肌醇二磷酸水解为肌醇三磷酸（IP3）和二酰基甘油。通过与腺苷酸环化酶的受体调节进行类比，有人提出“钙动员”受体可能与鸟嘌呤核苷酸结合蛋白（G蛋白）相互作用以调节磷脂酶C的活性。在此我们报告，在电通透的大鼠胰腺腺泡细胞中，响应于蛙皮素或卡巴胆碱，IP3的积累增加。GTP的稳定类似物（鸟苷5'-[γ-硫代]三磷酸和鸟苷5'-[β，γ-亚氨基]三磷酸）刺激IP3的积累并增强蛙皮素和卡巴胆碱的作用。这种协同作用证明了受体、G蛋白和磷脂酶C之间的相互作用。在产生对将受体与腺苷酸环化酶偶联的蛋白质Gi和Gs进行大量共价修饰的条件下，用百日咳毒素或霍乱毒素对细胞进行预处理不会影响这些反应。因此我们得出结论，在外分泌胰腺中将受体与磷脂酶C偶联的G蛋白可能既不是Gi也不是Gs；相反，我们提出一种不同的G蛋白介导这种效应。
