Cai Y C, Ma L, Fan G H, Zhao J, Jiang L Z, Pei G
Shanghai Institute of Cell Biology, Chinese Academy of Sciences, People's Republic of China.
Mol Pharmacol. 1997 Apr;51(4):583-7. doi: 10.1124/mol.51.4.583.
Coadministration of antagonists of N-methyl-D-aspartate (NMDA) receptor and opioids has been shown to prevent development of opiate tolerance in animal and clinical studies, but its cellular and molecular mechanisms are not understood. In this study, the effect of NMDA on delta-opioid receptor (DOR)-mediated signal transduction was investigated in neuroblastoma x glioma NG108-15 cells that functionally express both DOR and NMDA receptors. Acute incubation of NG108-15 cells with NMDA, a specific agonist of NMDA receptor, significantly attenuated the ability of DOR agonist [D-Pen2, D-Pen5]-enkephalin (DPDPE) to inhibit forskolin-stimulated cAMP production. The attenuation caused by NMDA was dose-dependent, and the EC50 of DPDPE increased 100-fold (from 4.6 nM to 500 nM) after NMDA treatment. The NMDA effect on responsiveness of delta-opioid receptors to DPDPE could be blocked by ketamine, a NMDA receptor-specific antagonist. This NMDA attenuation effect on DOR activity was also observed in neuronal primary cell cultures from fetal mouse brain but not in the Chinese hamster ovary cell line stably transfected with DOR alone. Interestingly, NMDA pretreatment reduced the cellular response to epinephrine but not to that of prostaglandin E1 in NG108-15 cells, which suggests differential modulation of NMDA on different G protein-coupled receptors. Pretreatment of NG108-15 cells with ketamine along with DPDPE greatly attenuated DPDPE-induced acute desensitization of DOR. Furthermore, the specific inhibitors of protein kinase C, either chelerythrine chloride or Go 6979, effectively blocked the NMDA effect, which indicates the involvement of protein kinase C in the process. In conclusion, the activation of NMDA receptors can attenuate acute responsiveness of DOR in neuronal cells, whereas its blockage leads to reduction of DOR desensitization. These results have thus provided an insight into cross-talk between NMDA and opioid signal transduction.
在动物和临床研究中，已表明N-甲基-D-天冬氨酸（NMDA）受体拮抗剂与阿片类药物共同给药可预防阿片耐受的形成，但其细胞和分子机制尚不清楚。在本研究中，在功能性表达DOR和NMDA受体的神经母细胞瘤x胶质瘤NG108-15细胞中，研究了NMDA对δ-阿片受体（DOR）介导的信号转导的影响。用NMDA受体的特异性激动剂NMDA急性孵育NG108-15细胞，显著减弱了DOR激动剂[D-青霉胺2，D-青霉胺5]-脑啡肽（DPDPE）抑制福斯高林刺激的cAMP产生的能力。NMDA引起的减弱是剂量依赖性的，NMDA处理后DPDPE的EC50增加了100倍（从4.6 nM增加到500 nM）。NMDA受体特异性拮抗剂氯胺酮可阻断NMDA对δ-阿片受体对DPDPE反应性的影响。在来自胎鼠脑的神经元原代细胞培养物中也观察到了NMDA对DOR活性的这种减弱作用，但在仅稳定转染了DOR的中国仓鼠卵巢细胞系中未观察到。有趣的是，NMDA预处理降低了NG108-15细胞对肾上腺素的细胞反应，但未降低对前列腺素E1的反应，这表明NMDA对不同G蛋白偶联受体的调节存在差异。用氯胺酮和DPDPE预处理NG108-15细胞可大大减弱DPDPE诱导的DOR急性脱敏。此外，蛋白激酶C的特异性抑制剂，即氯化白屈菜红碱或Go 6979，可有效阻断NMDA的作用，这表明蛋白激酶C参与了该过程。总之，NMDA受体的激活可减弱神经元细胞中DOR的急性反应性，而其阻断则导致DOR脱敏的减少。因此，这些结果为NMDA与阿片信号转导之间的相互作用提供了见解。
