Muscarine, L-(+)-muscarine, or muscarin is a natural product found in certain mushrooms, particularly in Inocybe and Clitocybe species, such as the deadly C. dealbata. Mushrooms in the genera Entoloma and Mycena have also been found to contain levels of muscarine which can be dangerous if ingested. Muscarine has been found in harmless trace amounts in Boletus, Hygrocybe, Lactarius and Russula. Trace concentrations of muscarine are also found in Amanita muscaria, though the pharmacologically more relevant compound from this mushroom is the Z-drug-like alkaloid muscimol. A. muscaria fruitbodies contain a variable dose of muscarine, usually around 0.0003% fresh weight. This is very low and toxicity symptoms occur very rarely. Inocybe and Clitocybe contain muscarine concentrations up to 1.6%.
Muscarine is a nonselective agonist of the muscarinic acetylcholine receptors.
The name muscarine derives from that of Amanita muscaria, from which it was first isolated, by German chemists Oswald Schmiedeberg and Richard Koppe at the University of Dorpat, who reported their findings in 1869. The mushroom's specific name in turn comes from the Latin musca for fly because the mushroom was often used to attract and catch flies, hence its common name, "fly agaric".
Muscarine was the first parasympathomimetic substance ever studied and causes profound activation of the peripheral parasympathetic nervous system that may end in circulatory collapse and death. Being a quaternary ammonium salt, muscarine is less completely absorbed from the gastrointestinal tract than tertiary amines, and it does not cross the blood–brain barrier.
Muscarinic agonists activate muscarinic receptors while nicotinic agonists activate nicotine receptors. Both are direct-acting cholinomimetics; they produce their effects by binding to and activating cholinergic receptors.
Final proof of the structure was given by Franz Jellinek and colleagues in 1957 with the help of X-ray diffraction analysis; Jellinek further described the three-dimensional structure of the molecule using muscarine chloride.
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Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled receptor complexes in the cell membranes of certain neurons and other cells. They play several roles, including acting as the main end-receptor stimulated by acetylcholine released from postganglionic fibers in the parasympathetic nervous system. Muscarinic receptors are so named because they are more sensitive to muscarine than to nicotine.
Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral nervous system, muscle, and many other tissues of many organisms. At the neuromuscular junction they are the primary receptor in muscle for motor nerve-muscle communication that controls muscle contraction.
In biochemistry and pharmacology, receptors are chemical structures, composed of protein, that receive and transduce signals that may be integrated into biological systems. These signals are typically chemical messengers which bind to a receptor and produce physiological responses such as change in the electrical activity of a cell. For example, GABA, an inhibitory neurotransmitter inhibits electrical activity of neurons by binding to GABA_A receptors.
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