Opioid receptors (ORs) convert extracellular messages to signaling events by coupling to the heterotrimeric G proteins, Gα•βγ. Classic pharmacological methods, such as [³⁵S]GTPγS binding and inhibition of cyclic AMP production, allow for general opioid characterization, but they are subject to the varying endogenous Gα proteins in a given cell type. Bioluminescence resonance energy transfer (BRET) technology offers new insight by allowing the direct observation of Gα subunit–specific effects on opioid pharmacology. Using a Venus-tagged Gβγ and nanoluciferase-tagged truncated G protein receptor kinase 3, an increase in BRET signal correlated with OR activation mediated by a specific Gα protein. The magnitude of the BRET signal was normalized to the maximum response obtained with 10 µM 2-(3,4-dichlorophenyl)-N-methyl-N-[(1R,2R)-2-pyrrolidin-1-ylcyclohexyl]acetamide (U50,488) for the kappa OR (KOR). Opioids reached equilibrium with the KOR, and concentration-response curves were generated. Although the full agonists U50,488, salvinorin A, nalfurafine, and dynorphin peptides were equally efficacious regardless of the Gα subunit present, the concentration-response curves were leftward shifted when the KOR was signaling through Gαz compared with other Gαi/o subunits. In contrast, the Gα subunit distinctly affected both the efficacy and potency of partial kappa agonists, such as the benzomorphans, and the classic mu opioid antagonists, naloxone, naltrexone, and nalmefene. For example, (-)pentazocine had EC₅₀ values of 7.3 and 110 nM and maximal stimulation values of 79% and 35% when the KOR signaled through Gαz and Gαi1, respectively. Together, these observations suggest KOR pharmacology varies based on the specific Gα subunit coupled to the KOR.

中文翻译：

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Kappa 阿片受体通过 Gαz 信号传导的独特药理学特性，如生物发光共振能量转移所示。

阿片受体 (OR) 通过与异源三聚体 G 蛋白 G α • βγ偶联，将细胞外信息转化为信号事件。经典的药理学方法，例如 [ ³⁵ S] GTP γ S 结合和环 AMP 产生的抑制，允许进行一般的阿片类药物表征，但它们受给定细胞类型中不同的内源性 G α蛋白的影响。生物发光共振能量转移 (BRET) 技术允许直接观察 G α亚基对阿片类药物药理学的特异性影响，从而提供了新的见解。使用金星标记的 G βγ和纳米荧光素酶标记的截短 G 蛋白受体激酶 3，BRET 信号的增加与由特定 G α蛋白介导的 OR 激活相关。将 BRET 信号的大小标准化为使用 10 µM 2-(3,4-二氯苯基) -N-甲基-N -[(1 R ,2 R )-2-吡咯烷-1-基环己基]乙酰胺获得的最大响应(U50,488) 为 kappa OR (KOR)。阿片类药物与 KOR 达到平衡，并生成浓度-反应曲线。尽管完全激动剂 U50,488、salvinorin A、纳夫拉芬和强啡肽无论 G α亚基存在时，与其他 G α i/o 亚基相比，当 KOR 通过 G α z发出信号时，浓度-反应曲线向左移动。相比之下，G α亚基明显影响部分κ激动剂（如苯并吗啡烷）和经典 μ 阿片拮抗剂纳洛酮、纳曲酮和纳美芬的功效和效力。例如，当 KOR 分别通过 G α z 和 G α i1发出信号时，(-)喷他佐辛的 EC ₅₀值为 7.3 和 110 nM，最大刺激值为 79% 和 35% 。总之，这些观察结果表明 KOR 药理学根据与 KOR 偶联的特定 G α亚基而变化。