Development of Displacement Binding and GTPγS Scintillation Proximity Assays for the Identification of Antagonists of the μ-Opioid Receptor

This article describes the development of μ-opioid receptor (MOR) binding and GTPγS functional SPAs as improved screening tools for the identification of MOR antagonists. Opioid receptors are members of the seven-transmembrane G protein-coupled receptor (GPCR) family and are involved in the control of various aspects of human physiology, including pain, stress, reward, addiction, respiration, gastric motility, and pituitary hormone secretion. Activation of the MOR initiates intracellular signaling pathways leading to a reduction in intracellular cyclic AMP levels, inhibition of calcium channels, and activation of potassium channels resulting in a reduction of the excitability of neurons. Characterization of opioid receptor ligand binding has traditionally been accomplished through the use of low throughput filtration-based binding assays, whereas functional activity has been based upon cyclic AMP measurements or filtration-based GTPγS functional assays. This report describes the development of a MOR displ...