Mu opioid receptor

Mu opioid receptor (MOR) is a type of opioid receptor with high affinity for enkephalins and beta-endorphin but low affinity for dynorphins. It is also the principal target of the opioid drug morphine. The MOR is a G protein-coupled receptor that functions as a receptor for naturally occurring opioids as well as for synthetic drugs of abuse.

Structure

The MOR is a member of the opioid family of G-protein coupled receptors, and is encoded by the OPRM1 gene. It is a 400 amino acid polypeptide, with a molecular weight of approximately 43kDa. The receptor is made up of seven transmembrane alpha helices, with an extracellular N-terminus and an intracellular C-terminus.

Function

The MOR is primarily located in the central nervous system, where it plays a key role in pain perception, reward, and addiction. Activation of the MOR leads to analgesia, sedation, euphoria, physical dependence, and respiratory depression. The MOR also plays a role in the regulation of gastrointestinal motility, secretion, and vascular tone.

Pharmacology

The MOR is the primary target of most opioid drugs, including morphine, heroin, fentanyl, and methadone. These drugs mimic the action of endogenous opioids to produce analgesia and other effects. However, chronic use of these drugs can lead to tolerance, physical dependence, and addiction.

Clinical significance

The MOR is a major target in the treatment of acute and chronic pain. However, the use of MOR agonists is limited by side effects such as respiratory depression, constipation, and addiction. Research is ongoing to develop MOR agonists with reduced side effects, as well as MOR antagonists for the treatment of opioid addiction.

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