μ-opioid receptor

The μ-opioid receptors (MOR) are a class of opioid receptors with a high affinity for enkephalins and beta-endorphin, but a low affinity for dynorphins. They are also referred to as μ(mu)-opioid peptide (MOP) receptors. The prototypical μ-opioid receptor agonist is morphine, the primary psychoactive alkaloid in opium. It is an inhibitory G-protein coupled receptor that activates the Gi alpha subunit, inhibiting adenylate cyclase activity, lowering cAMP levels. A cryo-electron microscopy structure of the µ-opioid receptor–Gi protein complex was published in 2018. Three variants of the μ-opioid receptor are well characterized, though RT-PCR has identified up to 10 total splice variants in humans.