View source for Ligand-gated ion channel

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[[Image:LGIC.png|thumb|400px|Ligand-gated ion channel]]

The '''Ligand-gated ion channels''', also referred to as '''LGICs''', or '''ionotropic receptors''', are a group of intrinsic transmembrane ion channels that are opened or closed in response to binding of a chemical messenger, as opposed to [[voltage-gated ion channel]]s or [[stretch-activated ion channel]]s. 

==Regulation==
The [[ion channel]] is regulated by a [[ligand]] and is usually very selective to one or more ions like [[sodium|Na<sup>+</sup>]], [[potassium|K<sup>+</sup>]], [[calcium|Ca<sup>2+</sup>]], or [[chloride|Cl<sup>-</sup>]]. Such receptors located at [[synapse]]s convert the chemical signal of [[presynaptic]]ally released neurotransmitter directly and very quickly into a [[postsynaptic]] electrical signal. 

Many LGICs are additionally modulated by [[allosteric]] [[ligand]]s, by [[channel blockers]], [[ion]]s, or the [[membrane potential]].

==Example: nicotinic acetylcholine receptor==
The prototypic ligand-gated ion channel is the [[nicotinic acetylcholine receptor]]. It consists of a pentamer of protein subunits, with two binding sites for [[acetylcholine]], which, when bound, alter the receptor's configuration and cause an internal pore to open.  This pore, permeable to Na<sup>+</sup>, allows Na<sup>+</sup> ions to flow down their [[electrochemical gradient]] into the cell. With a sufficient number of channels opening at once, the intracellular Na<sup>+</sup> concentration rises to the point at which the positive charge within the [[cell (biology)|cell]] is enough to depolarize the [[cell membrane|membrane]], and an [[action potential]] is initiated.

==Classification and examples==
Many important ion channels are ligand-gated, and they show a great degree of homology at the genetic level. The Ligand-gated ion channels are classified into three superfamilies: 
===The [[Cys-loop receptors]]===
* anionic
** [[GABAA receptor|GABA]]<sub>A</sub>
** [[GABAC receptor|GABA]]<sub>C</sub>
** [[glycine|Glycine]]
* cationic
** 5-HT<sub>3</sub> [[5-HT3 receptor|serotonin receptor]]
** [[nicotinic acetylcholine receptor]]

===The ionotropic [[glutamate receptor]]s===
*[[NMDA receptor|NMDA]]
*[[Kainate receptor|Kainate]] 
*[[AMPA receptor|AMPA]]
===The [[Adenosine triphosphate|ATP]]-gated channels===
*[[P2X Receptor|P2X]]

==Clinical relevance==
''Ligand-gated ion channels'' are likely to be the major site at which [[anaesthetic]] agents have their effects, although unequivocal evidence of this is yet to be established. In particular, the [[GABA]] and [[NMDA]] receptors are affected by [[anaesthetic]] agents at concentrations similar to those used in clinical anaesthesia.



== See also ==
*[[Chronotropic]]
*[[Receptor (biochemistry)]]
*[[Glycine receptor]]
*[[P2X Receptor]]
*[[Sodium ion channel]]

== References ==
* {{cite journal|last=Connolly|first=CN|coauthors=Wafford KA|year=2004|title=The Cys-loop superfamily of ligand-gated ion channels: the impact of receptor structure on function|url=http://www.biochemsoctrans.org/bst/032/bst0320529.htm|journal=Biochem. Soc. Trans|issn=0300-5127|volume=32|issue=3|pages=529-534|pmid=15157178|accessdate=2007-06-08}}

== External links ==
* [http://www.ebi.ac.uk/compneur-srv/LGICdb/LGICdb.php Ligand-Gated Ion Channel database] at [[European Bioinformatics Institute]]. Verified availability April 11, 2007.

{{Ion channels}}
{{Ligand-gated ion channels}}
[[Category:Membrane biology]]
[[Category:Ion channels]]
[[Category:Ionotropic receptors]]
[[Category:Neurochemistry]]
[[Category:Molecular neuroscience]]

[[de:Ionotroper Rezeptor]]
[[fr:Récepteur ionotropique]]
[[pl:Receptor jonotropowy]]
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