WordNet

a cellular structure that is postulated to exist in order to mediate between a chemical agent that acts on nervous tissue and the physiological response
releasing or activated by acetylcholine or a related compound

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=sense organ / 受信装置

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/06/18 13:10:55」(JST)

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Acetylcholine

An acetylcholine receptor (abbreviated AChR) is an integral membrane protein that responds to the binding of acetylcholine, a neurotransmitter.

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.

Nicotinic acetylcholine receptors (nAChR, also known as "ionotropic" acetylcholine receptors) are particularly responsive to nicotine. The nicotine ACh receptor is also a Na+ and K+ ion channel
Muscarinic acetylcholine receptors (mAChR, also known as "metabotropic" acetylcholine receptors) are particularly responsive to muscarine.

Nicotinic and muscarinic are two main kinds of "cholinergic" receptors.

Receptor types

Molecular biology has shown that the nicotinic and muscarinic receptors belong to distinct protein superfamilies.

ACh and its receptors
Drug	Nm	Nn	M1	M2	M3
ACh, Carbachol, Methacholine, AChEi (Psysostigmine, Galantamine, Neostigmine, Pyridostigmine)	+	+	+	+	+
Nicotine, Varenicline	+	+
Succinylcholine	+/-
Atracurium, Vecuronium, Tubocurarine, Pancuronium	-
Epibatidine, DMPP		+
Trimethaphan, Mecamylamine, Bupropion, Dextromethophan, Hexamethonium		-
Muscarine, Oxotremorine, Bethanechol, Pilocarpine			+	+	+
Atropine, Tolterodine, Oxybutynin			-	-	-
Vedaclidine, Talsaclidine, Xanomeline, Ipatropium			+
Pirenzepine, Telenzepine			-
Methoctramin				-
Darifenacin, 4-DAMP, Darifenacin, Solifenacin					-

Nicotinic receptors are of two types: Nm and Nn. Nm is located in the neuromuscular junction which causes the contraction of skeletal muscles by way of end-plate potential (EPPs). Nn causes depolarization in autonomic ganglia resulting in post ganglionic impulse. Nicotinic receptors cause the release of catecholamine from the adrenal medulla, and also site specific excitation or inhibition in brain. Both Nm and Nn are Na + and k + channel linked but Nn is also linked with an extra Ca ++ channel.

nAChR

The nAChRs are ligand-gated ion channels, and, like other members of the "cys-loop" ligand-gated ion channel superfamily, are composed of five protein subunits symmetrically arranged like staves around a barrel. The subunit composition is highly variable across different tissues. Each subunit contains four regions which span the membrane and consist of approximately 20 amino acids. Region II which sits closest to the pore lumen, forms the pore lining. ^[1]

Binding of acetylcholine to the N termini of each of the two alpha subunits results in the 15° rotation of all M2 helices.^[2] The cytoplasm side of the nAChR receptor has rings of high negative charge that determine the specific cation specificity of the receptor and remove the hydration shell often formed by ions in aqueous solution. In the intermediate region of the receptor, within the pore lumen, valine and leucine residues (Val 255 and Leu 251) define a hydrophobic region through which the dehydrated ion must pass.^[3]

The nAChR is found at the edges of junctional folds at the neuromuscular junction on the postsynaptic side; it is activated by acetylcholine release across the synapse. The diffusion of Na⁺ and K⁺ across the receptor causes depolarization, the end-plate potential, that opens voltage-gated sodium channels, which allows for firing of the action potential and potentially muscular contraction.

mAChR

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. The muscarine cholinergic receptor activates a G-protein when bound to extracellular ACh. The alpha subunit of the G-protein deactivates adenylate cyclase while the beta-gamma subunit activates the K-channels and therefore hyperpolarize the cell. This causes a decrease in cardiac activity.

Role in health and disease

Nicotinic acetylcholine receptors can be blocked by curare, hexamethonium and toxins present in the venoms of snakes and shellfishes, like α-bungarotoxin. Drugs such as the neuromuscular blocking agents bind reversibly to the nicotinic receptors in the neuromuscular junction and are used routinely in anaesthesia.

Nicotinic receptors are the primary mediator of the effects of nicotine. In myasthenia gravis, the receptor at NMJ is targeted by antibodies, leading to muscle weakness. Muscarinic acetylcholine receptors can be blocked by the drugs atropine and scopolamine.

Congenital myasthenic syndrome (CMS) is an inherited neuromuscular disorder caused by defects of several types at the neuromuscular junction. Postsynaptic defects are the most frequent cause of CMS and often result in abnormalities in nicotinic acetylcholine receptors. The majority of mutations causing CMS are found in the AChR subunits genes.^[4]

Out of all mutations associated with CMS, more than half are mutations in one of the four genes encoding the adult acetylcholine receptor subunits. Mutations of the AChR often result in endplate deficiency. Most of the mutations of the AChR are mutations of the CHRNE gene. The CHRNE gene codes for the epsilon subunit of the AChR. Most mutations are autosomal recessive loss-of-function mutations and as a result there is endplate AChR deficiency. CHRNE is associated with changing the kinetic properties of the AChR. ^[5] One type of mutation of the epsilon subunit of the AChR introduces an Arg into the binding site at the α/ε subunit interface of the receptor. The addition of a cationic Arg into the anionic environment of the AChR binding site greatly reduces the kinetic properties of the receptor. The result of the newly introduced ARG is a 30-fold reduction of agonist affinity, 75-fold reduction of gating efficiency, and an extremely weakened channel opening probability. This type of mutation results in an extremely fatal form of CMS. ^[6]

References

^ Pohanka, M (2012). "Alpha7 Nicotinic Acetylcholine Receptor Is a Target in Pharmacology and Toxicology". International Journal of Molecular Sciences 13 (2): 2219–2238. doi:10.3390/ijms13022219. PMC 3292018. PMID 22408449.
^ Doyle DA (2004). "Structural changes during ion channel gating". Trends Neurosci. 27 (6): 298–302. doi:10.1016/j.tins.2004.04.004. PMID 15165732.
^ Miyazawa A, Fujiyoshi Y, Unwin N (2003). "Structure and gating mechanism of the acetylcholine receptor pore". Nature 423 (6943): 949–55. doi:10.1038/nature01748. PMID 12827192.
^ Cossins, J.; Burke, G.; Maxwell, S.; Spearman, H.; Man, S.; Kuks, J.; Vincent, A.; Palace, J.; Fuhrer, C.; Beeson, D. (2006). "Diverse molecular mechanisms involved in AChR deficiency due to rapsyn mutations". Brain 129 (10): 2773–2783. doi:10.1093/brain/awl219. PMID 16945936. edit
^ Abicht, A.; Dusl, M.; Gallenmüller, C.; Guergueltcheva, V.; Schara, U.; Della Marina, A.; Wibbeler, E.; Almaras, S.; Mihaylova, V.; Von Der Hagen, M.; Huebner, A.; Chaouch, A.; Müller, J. S.; Lochmüller, H. (2012). "Congenital myasthenic syndromes: Achievements and limitations of phenotype-guided gene-after-gene sequencing in diagnostic practice: A study of 680 patients". Human Mutation 33 (10): 1474–1484. doi:10.1002/humu.22130. PMID 22678886. edit
^ Shen, X. -M.; Brengman, J. M.; Edvardson, S.; Sine, S. M.; Engel, A. G. (2012). "Highly fatal fast-channel syndrome caused by AChR subunit mutation at the agonist binding site". Neurology 79 (5): 449–454. doi:10.1212/WNL.0b013e31825b5bda. PMC 3405251. PMID 22592360. edit

External links

Acetylcholine receptor: PMAP The Proteolysis Map-animation
Acetylcholine Receptors at the US National Library of Medicine Medical Subject Headings (MeSH)
Acetlycholine Receptor: Molecule of The Month by David Goodsell
Acetylcholine receptors: muscarinic and nicotinic by Flavio Guzman
ANS receptors-overview

UpToDate Contents

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English Journal

Expression of the ghrelin receptor gene in neurons of the medulla oblongata of the rat.

Bron R, Yin L, Russo D, Furness JB.SourceDepartment of Anatomy & Neuroscience, University of Melbourne, Parkville, Victoria 3010, Australia.
The Journal of comparative neurology.J Comp Neurol.2013 Aug 15;521(12):2680-702. doi: 10.1002/cne.23309.
There is ambiguity concerning the distribution of neurons that express the ghrelin receptor (GHSR) in the medulla oblongata. In the current study we used a sensitive nonradioactive method to investigate GHSR mRNA distribution by in situ hybridization. Strong expression of the GHSR gene was confirmed
PMID 23348715

Involvement of dorsal hippocampal and medial septal nicotinic receptors in cross state-dependent memory between WIN55, 212-2 and nicotine or ethanol in mice.

Alijanpour S, Rezayof A.SourceDepartment of Animal Biology, School of Biology and Center of Excellence in Phylogeny of Living, College of Science, University of Tehran, Tehran, Iran.
Neuroscience.Neuroscience.2013 Aug 15;245:61-73. doi: 10.1016/j.neuroscience.2013.04.030. Epub 2013 Apr 23.
The present study examined whether nicotinic acetylcholine receptors (nAChRs) of the CA1 regions of the dorsal hippocampus and medial septum (MS) are involved in cross state-dependent memory retrieval between WIN55, 212-2 (WIN, a non-selective CB1/CB2 receptor agonist) and nicotine or ethanol. Memor
PMID 23624371

Cholinergic drugs as therapeutic tools in inflammatory diseases: participation of neuronal and non-neuronal cholinergic systems.

Sales ME.SourceCentro de Estudios Farmacológicos y Botánicos (CEFYBO)-CONICET, Segunda Cátedra de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155 piso 16 sector izq. Buenos Aires, Argentina, CABA, CP 1121. msales@fmed.uba.ar
Anti-inflammatory & anti-allergy agents in medicinal chemistry.Antiinflamm Antiallergy Agents Med Chem.2013 Aug 1;12(2):109-16.
Acetylcholine (ACh) is synthesized by choline acetyltransferase (ChAT) from acetylcoenzime A and choline. This reaction occurs not only in pre-ganglionic fibers of the autonomic nervous system and post-ganglionic parasympathetic nervous fibers but also in non neuronal cells. This knowledge led to ex
PMID 23360259

Japanese Journal

Critical roles of mecamylamine-sensitive mushroom body neurons in insect olfactory learning

Watanabe Hidehiro,Matsumoto Chihiro Sato,Nishino Hiroshi,Mizunami Makoto
Neurobiology of Learning and Memory 95(1), 1-13, 2011-01
… In insects, cholinergic neurons are thought to transmit olfactory conditioned stimulus (CS) to the sites for associating the CS with unconditioned stimulus (US), but the types of acetylcholine (ACh) receptor used by neurons participating in the association have not been determined. … In cockroaches, a type of nicotinic ACh receptor specifically antagonized by mecamylamine (MEC) has been characterized. …
NAID 120002834739

Adenine Sulfate Improves Cardiac Function and the Cardiac Cholinergic System After Myocardial Infarction in Rats

Sun Lei,Lu Jun,Yu Xiao-Jiang,Li Dong-Ling,Xu Xiao-Li,Wang Bing,Ren Ke-Yu,Liu Jian-Kang,Zang Wei-Jin
Journal of Pharmacological Sciences 115(2), 205-213, 2011
… Here, we investigate whether adenine sulfate can preserve cardiac function and the cholinergic system against MI. … The muscarinic M2 receptor and cholinesterase-positive nerves were semi-quantified by immunochemical and histochemical staining. … The amelioration was accompanied by a reversal of the infarction-induced reduction of cholinesterase-positive nerves and M2-receptor expression and Bmax in the adenine sulfate high dose group. …
NAID 130000439943

★リンクテーブル★

リンク元	「ACh receptor」「cholinoceptor」「コリン受容体」「コリン作動性受容体」「コリンレセプター」
拡張検索	「nicotinic cholinergic receptors」
関連記事	「cholinergic」