Hertting G, Wurster S, Allgaier C
Institute of Pharmacology, University of Freiburg, Federal Republic of Germany.
Ann N Y Acad Sci. 1990;604:289-304. doi: 10.1111/j.1749-6632.1990.tb32001.x.
Activation of alpha 2-adrenoceptors, opioid, A1-adenosine, and PGE receptors inhibited the stimulation-induced [3H]noradrenaline release in brain tissue in a concentration-dependent manner. Under experimental conditions (360 pulses/3 Hz) where the released noradrenaline activated the presynaptic alpha 2-autoreceptors, the effects of the heteroreceptor (k-opioid, A1-adenosine, PGE) agonists were decreased. By avoiding autoinhibition by either blockade of the alpha 2-autoreceptors with yohimbine or stimulating the tissue with four pulses/100 Hz, the heteroreceptor-mediated inhibition of [3H]noradrenaline release was markedly increased. The dependence of the heteroreceptor-mediated inhibition of evoked noradrenaline release on the extent of alpha 2-autoreceptor activation suggests a common postreceptor signal transduction pathway. PTX-catalyzed [32P]ADP ribosylation of synaptosomal membrane proteins revealed three bands of polypeptides with molecular weights corresponding to the alpha subunits of Go (39,000) and the Gi proteins (40,000, 41,000). Pretreatment with NEM reduced the PTX-induced 32P labeling by alkylating the alpha subunits at or near the site that is ADP ribosylated by PTX in a concentration-dependent manner. K(+)-evoked release of [3H]noradrenaline from synaptosomes indicated the presynaptic localization of the PTX-sensitive G proteins coupled to alpha 2-, k-, and A1-receptors of noradrenergic nerve terminals. Electrically evoked [3H]noradrenaline release was only increased by PTX or NEM in a time- and concentration-dependent manner when autoinhibition was present. The alpha 2-, opioid, and A1-adenosine receptor-mediated inhibition of [3H]noradrenaline release was impaired similarly by PTX or NEM treatment. In contrast, the inhibitory effect of PGE2 remained unaffected. These results indicate that presynaptic alpha 2-, opioid, and A1-receptors but not PGE receptors of noradrenergic nerve terminals are linked to PTX-sensitive G proteins. The interaction between the alpha 2-autoreceptors and the PGE receptors therefore does not occur at the level of a common pool of G proteins but at some subsequent step of the signal transduction mechanism.
α2-肾上腺素能受体、阿片受体、A1-腺苷受体和前列腺素E受体的激活以浓度依赖的方式抑制了脑组织中刺激诱导的[3H]去甲肾上腺素释放。在实验条件下（360次脉冲/3Hz），释放的去甲肾上腺素激活了突触前α2-自身受体，此时异源受体（κ-阿片受体、A1-腺苷受体、前列腺素E受体）激动剂的作用减弱。通过用育亨宾阻断α2-自身受体或用4次脉冲/100Hz刺激组织来避免自身抑制，异源受体介导的[3H]去甲肾上腺素释放抑制作用明显增强。异源受体介导的诱发去甲肾上腺素释放抑制作用对α2-自身受体激活程度的依赖性表明存在一条共同的受体后信号转导途径。PTX催化的突触体膜蛋白的[32P]ADP核糖基化显示出三条多肽带，其分子量对应于Go的α亚基（39,000）和Gi蛋白（40,000、41,000）。用NEM预处理以浓度依赖的方式通过烷基化PTX进行ADP核糖基化的位点或其附近的α亚基来降低PTX诱导的32P标记。K(+)诱发的突触体中[3H]去甲肾上腺素释放表明与去甲肾上腺素能神经末梢的α2-、κ-和A1-受体偶联的PTX敏感G蛋白位于突触前。当存在自身抑制时，电诱发的[3H]去甲肾上腺素释放仅在时间和浓度依赖的方式上被PTX或NEM增加。PTX或NEM处理同样损害了α2-、阿片受体和A1-腺苷受体介导的[3H]去甲肾上腺素释放抑制作用。相反，前列腺素E2的抑制作用不受影响。这些结果表明，去甲肾上腺素能神经末梢的突触前α2-、阿片受体和A1-受体而非前列腺素E受体与PTX敏感G蛋白相联系。因此，α2-自身受体与前列腺素E受体之间的相互作用并非发生在共同的G蛋白池水平，而是发生在信号转导机制的某些后续步骤。
