Editing Ion channel (section)

==== Other gating ====

Gating also includes activation and inactivation by [[second messenger]]s from the inside of the [[cell membrane]] – rather than from outside the cell, as in the case for ligands.
* Some potassium channels:
** [[Inward-rectifier potassium ion channel|Inward-rectifier potassium channels]]: These channels allow potassium ions to flow into the cell in an "inwardly rectifying" manner: potassium flows more efficiently into than out of the cell. This family is composed of 15 official and 1 unofficial member and is further subdivided into 7 subfamilies based on homology. These channels are affected by intracellular [[Adenosine triphosphate|ATP]], PIP<sub>2</sub>, and [[G-protein]] βγ subunits. They are involved in important physiological processes such as pacemaker activity in the heart, insulin release, and potassium uptake in [[glia|glial cells]]. They contain only two transmembrane segments, corresponding to the core pore-forming segments of the K<sub>V</sub> and K<sub>Ca</sub> channels. Their α subunits form tetramers.
** [[Calcium-activated potassium channel]]s: This family of channels is activated by intracellular Ca<sup>2+</sup> and contains 8 members.
** [[Tandem pore domain potassium channel]]: This family of 15 members form what are known as [[leak channel]]s, and they display [[GHK current equation|Goldman-Hodgkin-Katz]] (open) [[rectifier|rectification]]. Contrary to their common name of 'Two-pore-domain potassium channels', these channels have only one pore but two pore domains per subunit.<ref>{{cite web|url=http://www.guidetopharmacology.org/GRAC/FamilyDisplayForward?familyId=79|title=Two P domain potassium channels|publisher=[[Guide to Pharmacology]]|access-date=2019-05-28}}</ref><ref name="Rang60">{{cite book|title=Pharmacology|url=https://archive.org/details/clinicalpharmaco00frcp|url-access=limited| vauthors = Rang HP |publisher=Churchill Livingstone|year=2003|isbn=978-0-443-07145-4|edition=8th|location=Edinburgh|page=[https://archive.org/details/clinicalpharmaco00frcp/page/n74 59]}}</ref>
* [[Two-pore channel]]s include ligand-gated and voltage-gated cation channels, so-named because they contain two pore-forming subunits. As their name suggests, they have two pores.<ref>{{cite journal | vauthors = Kintzer AF, Stroud RM | title = Structure, inhibition and regulation of two-pore channel TPC1 from Arabidopsis thaliana | journal = Nature | volume = 531 | issue = 7593 | pages = 258–62 | date = March 2016 | pmid = 26961658 | pmc = 4863712 | doi = 10.1038/nature17194 | quote = Other than Ca2+ and Na+ channels that are formed by four intramolecular repeats, together forming the tetrameric channel's pore, the new channel had just two Shaker-like repeats, each of which was equipped with one pore domain. Because of this unusual topology, this channel, present in animals as well as plants, was named Two Pore Channel1 (TPC1). | bibcode = 2016Natur.531..258K | biorxiv = 10.1101/041400 }}</ref><ref>{{cite journal | vauthors = Spalding EP, Harper JF | title = The ins and outs of cellular Ca(2+) transport | journal = Current Opinion in Plant Biology | volume = 14 | issue = 6 | pages = 715–20 | date = December 2011 | pmid = 21865080 | pmc = 3230696 | doi = 10.1016/j.pbi.2011.08.001 | quote = The best candidate for a vacuolar Ca2+ release channel is TPC1, a homolog of a mammalian voltage-gated Ca2+ channel that possesses two pores and twelve membrane spans. }}</ref><ref>{{cite journal | vauthors = Brown BM, Nguyen HM, Wulff H | title = Recent advances in our understanding of the structure and function of more unusual cation channels | journal = F1000Research | volume = 8 | pages = 123 | date = 2019-01-30 | pmid = 30755796 | pmc = 6354322 | doi = 10.12688/f1000research.17163.1 | quote = Organellar two-pore channels (TPCs) are an interesting type of channel that, as the name suggests, has two pores. | doi-access = free }}</ref><ref>{{cite journal | vauthors = Jammes F, Hu HC, Villiers F, Bouten R, Kwak JM | title = Calcium-permeable channels in plant cells | journal = The FEBS Journal | volume = 278 | issue = 22 | pages = 4262–76 | date = November 2011 | pmid = 21955583 | doi = 10.1111/j.1742-4658.2011.08369.x | s2cid = 205884593 | quote = The Arabidopsis two‐pore channel (AtTPC1) has been predicted to have 12 transmembrane helices and two pores (red lines). | doi-access = free }}</ref><ref>{{cite thesis|url=http://discovery.ucl.ac.uk/1335830/1/1335830.pdf|quote=It is believed that TPCs, with their two pores, dimerise to form a functional channel.|title=Molecular characterisation of NAADP-gated two-pore channels| first = Robert | last = Hooper | name-list-style = vanc |date=September 2011}}</ref>
* [[Light-gated ion channels|Light-gated channels]] like [[channelrhodopsin]] are directly opened by [[photon]]s.
* [[Mechanosensitive ion channel]]s open under the influence of stretch, pressure, shear, and displacement.
* [[Cyclic nucleotide-gated channels]]: This superfamily of channels contains two families: the cyclic nucleotide-gated (CNG) channels and the hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels. This grouping is functional rather than evolutionary.
** Cyclic nucleotide-gated channels: This family of channels is characterized by activation by either intracellular [[Cyclic adenosine monophosphate|cAMP]] or [[Cyclic guanosine monophosphate|cGMP]]. These channels are primarily permeable to monovalent cations such as K<sup>+</sup> and Na<sup>+</sup>. They are also permeable to Ca<sup>2+</sup>, though it acts to close them. There are 6 members of this family, which is divided into 2 subfamilies.
** Hyperpolarization-activated [[cyclic nucleotide-gated channels]]
* Temperature-gated channels: Members of the [[Trp channel|transient receptor potential ion channel]] superfamily, such as [[TRPV1]] or [[TRPM8]], are opened either by hot or cold temperatures.