Μ Opioid Receptors

From Proteopedia

The µ opioid receptor (MOR) is the mediator of opioid interactions with the body. It is a well characterized and prevalent protein. Opium is one of the oldest drugs in use in the world, with derivatives like morphine, heroin, and codeine which are among the most widely used recreational and clinical drugs. Opioid compounds are found throughout nature in plants and in endogenously produced horomones. Opioid receptors are mitigation points of pain within the body, that is why codeine and morphine are used as pain relievers because they are agonistic to the MOR. This makes the subject of the µ opioid receptor a topic of considerable conversation (Pan). The structure of the MOR is one that includes it in a large superfamily of globular protein coupled receptors (GPCR) which have seven transmembrane-spanning helices (Waldhoer). The location of these helices can be found on the plasma membranes of dendritic cells, the sarcolemma which composes the outer portion of muscle of a muscle cell, at points of focal adhesion, and more (P42866 UniProt). Presently there are 10 known variants within the human body of the MOR, however given their prevalence in cells there may be more yet to be discovered (Pan). There is still much to learn about MOR, their activation by opioids, and the connection to other proteins. There has been a traditional explanation of the MOR based on its interactions with GABA (gamma aminobutyrate) (Liao). GABA is an inhibitory neurotransmitter in adult mammalian brains and is a multifunctional molecule with situational functions acting mainly in the central nervous system. Depending on the situation GABA acts as an excitatory or deactivating signal to neurons (Watanabe). It has been established that the MOR when activated by opioids regulates the excitability (mediating pain) of neurons through interactions with GABA in such a way that it suppresses the release of GABA from inhibitory neurons through the changing on Cl- ion channeling and concentration (Liao). However, further research into the MOR has revealed action which challenges this classical function. Through activation of the MOR in synapses, opioids have been shown to actually collapse preexisting dendritic spines and receptors (Liao).