Control of the adenylate cyclase system by GABA_b receptors

为了阐明突触前抑制的机制，我们研究了GABA_b受体介导的信号转导。本研究项目的研究成果如下：1.GABAB受体与百日咳毒素敏感的GTP结合蛋白G_1和G_O在脑膜上偶联。N-乙基马来酰亚胺通过与百日咳毒素类似的机制将GABAB受体与GTP结合蛋白解偶联。G_i和G_o抑制钙调素刺激的环核苷酸磷酸二酯酶。GTP结合蛋白似乎以钙依赖的方式直接与钙调蛋白结合。建立了测定G_o(G_o&lt；α&gt；)亚基的高灵敏免疫分析方法。本文研究了G_o&lt；α&gt；在大鼠体内的组织和细胞分布。结果表明，G_o仅定位于神经组织和神经内分泌细胞。还建立了测定GTP结合蛋白&lt；β&gt；亚单位的免疫酶标法。脑组织中β&gt；亚基浓度高于Go&lt；α&gt；亚基。

To make clear the mechanism of presynaptic inhibition,the signal transduction mediated by GABA_b reseptors was investigated. The findings in this research project are as follows.1. GABA_b reseptors are coupled to pertussis toxin-sensitive GTP-binding proteins,G_i and G_o, in the brain membranes.2. N-Ethylmaleimide uncouples GABA_b reseptors from GTP-binding proteins by the similar mechanism of pertussis toxin.3. G_i and G_o inhibited calmodulin-stimulated cyclic nucleotide phosphodiesterase. GTP-binding proteins seem to bind directly to calmodulin in a Ca^<2+>-dependent manner.4. Highly sensitive immunoassay method for the quantification of the <alpha> subunit of G_o (G_o<alpha>) was developed. The tissue and cellular distridution of G_o<alpha> was investigated in the rat. The results indicate that G_o is localized exclusively in the nervous tissues and neuroendocrine cells.5. Immunoassya method for the quantification of the <beta> subunit of GTP-binding proreins was also developed. The concentrations of <beta> subunit were higher than those of G_o<alpha> in the brain.