Department of Biological Sciences and Geology, Queensboro Community College, Bayside, New York 11364-1497, United States.
Biochemistry. 2011 Apr 12;50(14):2829-37. doi: 10.1021/bi101701x. Epub 2011 Mar 17.
Prolonged morphine treatment induces extensive desensitization of the μ-opioid receptor (μOR) which is the G-protein-coupled receptor that primarily mediates the cellular response to morphine. To date, the molecular mechanism underlying this process is unknown. Here, we have used live cell fluorescence imaging to investigate whether prolonged morphine treatment affects the physical environment of μOR, or its coupling with G-proteins, in two neuronal cell lines. We find that chronic morphine treatment does not change the amount of enhanced yellow fluorescence protein (eYFP)-tagged μOR on the plasma membrane, and only slightly decreases its association with G-protein subunits. Additionally, morphine treatment does not have a detectable effect on the diffusion coefficient of eYFP-μOR. However, in the presence of another family member, the δ-opioid receptor (δOR), prolonged morphine exposure results in a significant increase in the diffusion rate of μOR. Number and brightness measurements suggest that μOR exists primarily as a dimer that will oligomerize with δOR into tetramers, and morphine promotes the dissociation of these tetramers. To provide a plausible structural context to these data, we used homology modeling techniques to generate putative configurations of μOR-δOR tetramers. Overall, our studies provide a possible rationale for morphine sensitivity.
长期吗啡治疗会导致 μ 阿片受体（μOR）的广泛脱敏，μOR 是主要介导吗啡细胞反应的 G 蛋白偶联受体。迄今为止，这一过程的分子机制尚不清楚。在这里，我们使用活细胞荧光成像技术研究了长期吗啡治疗是否会影响两种神经元细胞系中 μOR 的物理环境或其与 G 蛋白的偶联。我们发现，慢性吗啡处理不会改变质膜上增强型黄色荧光蛋白（eYFP）标记的 μOR 的数量，并且仅略微降低其与 G 蛋白亚基的结合。此外，吗啡处理对 eYFP-μOR 的扩散系数没有可检测的影响。然而，在另一个家族成员 δ 阿片受体（δOR）存在的情况下，长期暴露于吗啡会导致 μOR 的扩散速率显著增加。数量和亮度测量表明 μOR 主要作为二聚体存在，它将与 δOR 形成四聚体，而吗啡促进这些四聚体的解离。为了为这些数据提供一个合理的结构背景，我们使用同源建模技术生成了 μOR-δOR 四聚体的可能构象。总的来说，我们的研究为吗啡敏感性提供了一个合理的依据。
