Opioid Receptor Oligomerization: Detection and Functional Characterization of Interacting Receptors

Opioid receptors are members of the G-protein coupled receptor (GPCR) family characterized by the presence of seven transmembrane domains. These receptors are classified as mu (μ), delta (δ), and kappa (κ). Activation of these receptors leads to uncoupling of the inhibitory G-proteins (G_i ) followed by the activation of multiple signal transduction pathways including the inhibition of adenylyl cyclase, modulation of inwardly rectifying K⁺ channels or voltage-dependent calcium channels and regulation of mitogen-activated protein (MAP) kinase activity (1 –4 ).