Martin N A, Prather P L
Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA.
Mol Pharmacol. 2001 Apr;59(4):774-83. doi: 10.1124/mol.59.4.774.
mu- and delta-Opioid agonists interact in a synergistic manner to produce analgesia in several animal models. Additionally, receptor binding studies using membranes derived from brain tissue indicate that interactions between mu- and delta-opioid receptors might be responsible for the observation of multiple opioid receptor subtypes. To examine potential interactions between mu- and delta-opioid receptors, we examined receptor binding and functional characteristics of mu-, delta-, or both mu- and delta-opioid receptors stably transfected in rat pituitary GH(3) cells (GH(3)MOR, GH(3)DOR, and GH(3)MORDOR, respectively). Saturation and competition binding experiments revealed that coexpression of mu- and delta-opioid receptors resulted in the appearance of multiple affinity states for mu- but not delta-opioid receptors. Additionally, coadministration of selective mu- and delta-opioid agonists in GH(3)MORDOR cells resulted in a synergistic competition with [(3)H][D-Pen(2,5)]enkephalin (DPDPE) for delta-opioid receptors. Finally, when equally effective concentrations of [D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin (DAMGO) and two different delta-opioid agonists (DPDPE or 2-methyl-4a alpha-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a alpha-octahydroquinolino-[2,3,3-g]-isoquinoline; TAN67) were coadministered in GH(3)MORDOR cells, a synergistic inhibition of adenylyl cyclase activity was observed. These results strongly suggest that cotransfection of mu- and delta-opioid receptors alters the binding and functional characteristics of the receptors. Therefore, we propose that the simultaneous exposure of GH(3)MORDOR cells to selective mu- and delta-opioid agonists produces an interaction between receptors resulting in enhanced receptor binding. This effect is translated into an augmented ability of these agonists to inhibit adenylyl cyclase activity. Similar interactions occurring in neurons that express both mu- and delta-opioid receptors could explain observations of multiple opioid receptor subtypes in receptor binding studies and the synergistic interaction of mu- and delta-opioids in analgesic assays.
μ-阿片受体激动剂和δ-阿片受体激动剂以协同方式相互作用，在多种动物模型中产生镇痛作用。此外，使用源自脑组织的膜进行的受体结合研究表明，μ-阿片受体和δ-阿片受体之间的相互作用可能是观察到多种阿片受体亚型的原因。为了研究μ-阿片受体和δ-阿片受体之间的潜在相互作用，我们检测了稳定转染于大鼠垂体GH(3)细胞中的μ-阿片受体、δ-阿片受体或二者（分别为GH(3)MOR、GH(3)DOR和GH(3)MORDOR）的受体结合及功能特性。饱和结合和竞争结合实验显示，μ-阿片受体和δ-阿片受体的共表达导致μ-阿片受体出现多种亲和力状态，而δ-阿片受体则未出现。此外，在GH(3)MORDOR细胞中联合给予选择性μ-阿片受体激动剂和δ-阿片受体激动剂，会与[(3)H][D-Pen(2,5)]脑啡肽（DPDPE）对δ-阿片受体产生协同竞争。最后，当在GH(3)MORDOR细胞中共同给予等效浓度的[D-Ala(2),N-MePhe(4),Gly-ol(5)]脑啡肽（DAMGO）和两种不同的δ-阿片受体激动剂（DPDPE或2-甲基-4aα-(3-羟基苯基)-1,2,3,4,4a,5,12,12aα-八氢喹啉并-[2,3,3-g]-异喹啉；TAN67）时，观察到对腺苷酸环化酶活性的协同抑制作用。这些结果强烈表明，μ-阿片受体和δ-阿片受体的共转染改变了受体的结合及功能特性。因此，我们提出，GH(3)MORDOR细胞同时暴露于选择性μ-阿片受体激动剂和δ-阿片受体激动剂会导致受体之间的相互作用，从而增强受体结合。这种效应转化为这些激动剂抑制腺苷酸环化酶活性的能力增强。在同时表达μ-阿片受体和δ-阿片受体的神经元中发生的类似相互作用，可以解释在受体结合研究中观察到的多种阿片受体亚型以及在镇痛试验中μ-阿片受体和δ-阿片受体的协同相互作用。
