Opioid receptors (ORs) are among the best-studied G protein-coupled receptors due to their involvement in neurological disorders and important role in pain treatment. Contrary to the classical monomeric model, indirect evidence suggests that ORs might form dimers, which could be endowed with a distinct pharmacological profile, and, thus, be targeted to develop innovative pharmacological therapies. However, direct evidence for the spontaneous formation of OR dimers in living cells under physiological conditions is missing. Despite a growing interest in the κ opioid receptor (KOR), KOR-selective fluorescent probes are particularly scarce in the literature. Herein, we present the first set of fluorescent KOR-selective probes with antagonistic properties. Two of these were employed in single-molecule microscopy (SMM) experiments to investigate KOR homodimerization, localization, and trafficking. Our findings indicate that most KORs labeled with the new fluorescent probes are present as apparently freely diffusing monomers on the surface of a simple cell model.

中文翻译：

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通过使用新的拮抗荧光探针的单分子显微镜研究非活性状态κ阿片受体同质化。

阿片类药物受体（ORs）因其参与神经系统疾病和在疼痛治疗中的重要作用而成为研究最深入的G蛋白偶联受体。与经典单体模型相反，间接证据表明OR可能会形成二聚体，而二聚体可能具有独特的药理学特征，因此有针对性地开发创新的药理学疗法。但是，缺少在生理条件下在活细胞中自发形成OR二聚体的直接证据。尽管人们对κ阿片受体（KOR）的兴趣日益增长，但在文献中特别缺乏KOR选择性荧光探针。在这里，我们介绍了具有拮抗特性的第一组荧光KOR-选择性探针。其中的两个被用于单分子显微镜（SMM）实验中，以研究KOR同型二聚化，定位和运输。我们的发现表明，用新的荧光探针标记的大多数KOR以明显的自由扩散单体的形式存在于简单细胞模型的表面。