Narita M
Department of Anesthesiology, Medical College of Wisconsin, Milwaukee 53226, USA.
Nihon Shinkei Seishin Yakurigaku Zasshi. 1998 Aug;18(4):107-16.
Recent cloning and expression studies have revealed that the opioid mu-, delta-, kappa- and orphan receptors are seven-transmembrane domain receptors whose actions are mediated through activation of guanine nucleotide binding protein (G-protein). The activation of G-proteins by the opioid receptor can be measured by assessing agonist stimulation of membrane binding of the non-hydrolyzable analog of guanosine triphosphate (GTP), guanosine-5'-O-(3-[35S] thio) triphosphate ([35S] GTP gamma S). Our recent data suggest that 1) the level of spinal mu-, delta-, kappa- and orphan-receptor agonist-stimulated [35S] GTP gamma S binding closely parallels that of receptor binding densities, 2) the neuroanatomical distribution of opioid agonist-stimulated [35S] GTP gamma S binding relates to receptor binding distribution, 3) newly isolated opioid peptides, endomorphin-1 and -2, can activate G-proteins by specific stimulation of mu-receptors and act as partial agonists with moderate catalytic efficacies, 4) mu-receptor densities could be rate-limiting steps in the G-protein activation by mu-agonists in the spinal cord region. In conclusion, opioid agonist-stimulated [35S] GTP gamma S binding can provide a functional method to localize receptors not only by their ability to bind ligands, but also according to their ability to activate an intracellular signal transducer.
最近的克隆和表达研究表明，阿片类μ、δ、κ和孤儿受体是七跨膜结构域受体，其作用通过鸟嘌呤核苷酸结合蛋白（G蛋白）的激活介导。阿片受体对G蛋白的激活可通过评估激动剂对三磷酸鸟苷（GTP）的不可水解类似物鸟苷-5'-O-(3-[35S]硫代)三磷酸（[35S]GTPγS）膜结合的刺激来测定。我们最近的数据表明：1）脊髓μ、δ、κ和孤儿受体激动剂刺激的[35S]GTPγS结合水平与受体结合密度密切平行；2）阿片激动剂刺激的[35S]GTPγS结合的神经解剖分布与受体结合分布相关；3）新分离的阿片肽内吗啡肽-1和-2可通过特异性刺激μ受体激活G蛋白，并作为具有中等催化效率的部分激动剂；4）在脊髓区域，μ受体密度可能是μ激动剂激活G蛋白的限速步骤。总之，阿片激动剂刺激的[35S]GTPγS结合不仅可以根据受体结合配体的能力，还可以根据其激活细胞内信号转导器的能力，提供一种定位受体的功能方法。
