An acetylcholine receptor (abbreviated AChR) is an integral membrane protein that responds to the binding of the neurotransmitter acetylcholine. Integral membrane protein of the transmembrane type An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that in most cases spans the biological membrane with which it is associated (especially the plasma membrane) or which, in any case, is sufficiently embedded in the membrane to remain... Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between a neuron and another cell. ... The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. ...

Classification

Like other transmembrane receptors, acetylcholine receptors are classified according to their "pharmacology", or according to their relative affinities and sensitivities to different molecules. Although all acetylcholine receptors, by definition, respond to acetylcholine, they respond to other molecules as well. Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ...

• nicotinic acetylcholine receptors (nAChR, also known as "ionotropic" acetylcholine receptors) are particularly responsive to nicotine
• muscarinic acetylcholine receptors (mAChR, also known as "metabotropic" acetylcholine receptors) are particularly responsive to muscarine.

Nicotinic acetylcholine receptors, or nAChRs, are ionotropic receptors that form ion channels in cells plasma membranes. ... Ionotropic receptor (also ligand gated ion channel) are a subclass of transmembrane receptors. ... Nicotine is an organic compound, a pyrrolidine-like alkaloid found naturally in the nightshade family of plants, such as tobacco and tomatoes. ... Muscarinic receptors are those membrane-bound acetylcholine receptors that are more sensitive to muscarine than to nicotine. ... Based on their structural and functional characteristics, neurotransmitter receptors can be classified into two broad categories: metabotropic and ionotropic receptors. ... Muscarine, L-(+)-muscarine, or muscarin is a natural product found in certain mushrooms, particularly in Inocybe and Clitocybe species. ...

Receptor types

Molecular biology has shown that the nicotinic and muscarinic receptors belong to distinct protein superfamilies. Molecular biology is the study of biology at a molecular level. ... In biology, a superfamily is a taxonomic grade intermediate between suborder and family. ...

The nAChRs are ion channels, and, like other members of the "cys-loop" ligand-gated ion channel superfamily, are composed of five protein subunits arranged like staves around a barrel. The subunit composition is highly variable across different tissues. Each channel contains two alpha subunits, a beta, a gamma, and a delta. Binding of acetylcholine to the N termini of each of the alpha subunits results in activation of the channel. Each subunit contains four regions named M1, M2, M3, and M4, which probably span the membrane. The M2 region, which sits closest to the pore lumen, forms the pore lining. The pore formed when the nAChR channel is open is permeable to both Na+ and K+ ions. Another, unrelated ion channeling process is part of ion implantation. ... Ligand-gated ion channel is a broad term that refers to any ion channel that is gated (i. ... In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or coassembles) with other protein molecules to form a multimeric or oligomeric protein. ...

In contrast, the mAChRs are not ion channels, but belong instead to the superfamily of G-protein-coupled receptors that activate other ionic channels via a second messenger cascade. G-protein-coupled receptors (GPCRs), also known as seven transmembrane receptors, heptahelical receptors, or 7TM receptors), are a protein family of transmembrane receptors that transduce an extracellular signal (ligand binding) into an intracellular signal (G protein activation). ... In biology, second messengers are low-weight diffusible molecules that are used in signal transduction to relay a signal within a cell. ...

Role in health and disease

Nicotinic acetylcholine receptors can be blocked by curare and toxins present in the venoms of snakes and shellfishes. Drugs such as the neuromuscular blocking agents bind reversibly to the nicotinic receptors in the neuromuscular junction and are used routinely in anaesthesia. Strychnos toxifera by Koehler 1887 Curare is a substance containing the alkaloid D-tubocurarine. ... Superfamilies and Families Henophidia Aniliidae Anomochilidae Boidae Bolyeriidae Cylindrophiidae Loxocemidae Pythonidae Tropidophiidae Uropeltidae Xenopeltidae Typhlopoidea Anomalepididae Leptotyphlopidae Typhlopidae Xenophidia Acrochordidae Atractaspididae Colubridae Elapidae Hydrophiidae Viperidae Snakes (from Old English snaca, and ultimately from PIE base *snag- or *sneg-, to crawl), also known as ophidians, are cold blooded legless reptiles closely... Shellfish is a term used to describe shelled molluscs and crustaceans used as food. ... In medicine, a muscle relaxant is a drug that causes skeletal muscle contraction to cease. ... A neuromuscular junction is the junction of the axon terminal of a motoneuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscles surface. ...

Nicotinic receptors are the main mediator of nicotine and tobacco addiction. In myasthenia gravis, the receptor is targeted by antibodies, leading to muscle weakness. Muscarinic acetylcholine receptors can be blocked by the drugs atropine and scopolamine. Myasthenia gravis (MG, Latin: grave muscle weakness) is a neuromuscular disease leading to fluctuating weakness and fatiguability. ... Schematic of antibody binding to an antigen An antibody is a protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... Atropine is a tropane alkaloid extracted from the deadly nightshade (Atropa belladonna) and other plants of the family Solanaceae. ... Scopolamine, also known as hyoscine, is an tropane alkaloid drug obtained from plants of the Solanaceae family (Nightshade), such as henbane or jimson weed (Datura stramonium). ...