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'''Inward-rectifier potassium channels''' ('''K<sub>ir</sub>''', '''IRK''') are a specific subset of [[potassium channel]]s. To date, seven subfamilies have been identified in various mammalian cell types,<ref name="Kubo">{{cite journal | vauthors = Kubo Y, Adelman JP, Clapham DE, Jan LY, Karschin A, Kurachi Y, Lazdunski M, Nichols CG, Seino S, Vandenberg CA | title = International Union of Pharmacology. LIV. Nomenclature and Molecular Relationships of Inwardly Rectifying Potassium Channels | journal = Pharmacological Reviews | volume = 57 | issue = 4 | pages = 509–26 | date = December 2005 | pmid = 16382105 | doi = 10.1124/pr.57.4.11 | authorlink8 = Colin Nichols }}</ref> plants,<ref name="pmid8582318">{{cite journal | vauthors = Hedrich R, Moran O, Conti F, Busch H, Becker D, Gambale F, Dreyer I, Küch A, Neuwinger K, Palme K | title = Inward rectifier potassium channels in plants differ from their animal counterparts in response to voltage and channel modulators | journal = European Biophysics Journal | volume = 24 | issue = 2 | pages = 107–15 | year = 1995 | pmid = 8582318 | doi = 10.1007/BF00211406 }}</ref> and bacteria.<ref name="tcdb.org">{{Cite web|url = http://www.tcdb.org/search/result.php?tc=1.A.2|title = 1.A.2 Inward Rectifier K Channel (IRK-C) Family|website = TCDB|access-date = 2016-04-09}}</ref> They are the targets of multiple toxins, and malfunction of the channels has been implicated in several diseases.<ref name="Abraham">{{cite journal | vauthors = Abraham MR, Jahangir A, Alekseev AE, Terzic A | title = Channelopathies of inwardly rectifying potassium channels | journal = FASEB Journal | volume = 13 | issue = 14 | pages = 1901–10 | date = November 1999 | pmid = 10544173 | url = http://www.fasebj.org/cgi/content/full/13/14/1901 | doi = 10.1096/fasebj.13.14.1901 }}</ref> IRK channels possess a pore domain, homologous to that of [[voltage-gated ion channel]]s, and flanking [[transmembrane domain |transmembrane segments]] (TMSs). They may exist in the membrane as homo- or heterooligomers and each monomer possesses between 2 and 4 TMSs. In terms of function, these proteins transport [[potassium|potassium (K<sup>+</sup>)]], with a greater tendency for K<sup>+</sup> uptake than K<sup>+</sup> export.<ref name="tcdb.org"/> The process of inward-rectification was discovered by [[Denis Noble]] in cardiac muscle cells in 1960s and by [[Richard Adrian, 2nd Baron Adrian|Richard Adrian]] and [[Alan Lloyd Hodgkin|Alan Hodgkin]] in 1970 in skeletal muscle cells.<ref>{{
==Overview of inward rectification==
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== Regulation ==
Voltage-dependence may be regulated by external K<sup>+</sup>, by internal Mg<sup>2+</sup>, by internal [[Adenosine triphosphate|ATP]] and/or by [[G protein|G-proteins]]. The P domains of IRK channels exhibit limited sequence similarity to those of the [[Voltage-gated ion channel (VIC) family|VIC family]]. Inward rectifiers play a role in setting cellular membrane potentials, and closing of these channels upon depolarization permits the occurrence of long duration action potentials with a plateau phase. Inward rectifiers lack the intrinsic voltage sensing helices found in many VIC family channels. In a few cases, those of Kir1.1a, Kir6.1 and Kir6.2, for example, direct interaction with a member of the ABC superfamily has been proposed to confer unique functional and regulatory properties to the heteromeric complex, including sensitivity to ATP. These ATP-sensitive channels are found in many body tissues. They render channel activity responsive to the cytoplasmic ATP/ADP ratio (increased ATP/ADP closes the channel). The human SUR1 and SUR2 [[sulfonylurea]] receptors (spQ09428 and Q15527, respectively) are the ABC proteins that regulate both the Kir6.1 and Kir6.2 channels in response to ATP, and CFTR ([http://www.tcdb.org/search/result.php?tc=3.A.1.208.4 TC #3.A.1.208.4]) may regulate Kir1.1a.<ref>{{
== Structure ==
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