Editing Gap junction (section)

{{Short description|Cell-cell junction composed of innexins or connexins}}
{{Tone|date=April 2024}}
{{Infobox anatomy
| Name        = Gap junction
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| Image       = Gap_cell_junction-en.svg
| Caption     = Vertebrate gap junction
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| Caption2    =
| Precursor   =
| System      =
| Artery      =
| Vein        =
| Nerve       =
| Lymph       =
}}
'''Gap junctions''' are [[Membrane channel|membrane channels]] between adjacent cells that allow the direct exchange of cytoplasmic substances, such  small molecules, substrates, and metabolites.<ref name="Talukdar">{{cite journal |last1=Talukdar |first1=S |last2=Emdad |first2=L |last3=Das |first3=SK |last4=Fisher |first4=PB |title=GAP junctions: multifaceted regulators of neuronal differentiation. |journal=Tissue Barriers |date=2 January 2022 |volume=10 |issue=1 |pages=1982349 |doi=10.1080/21688370.2021.1982349 |pmid=34651545|pmc=8794256 }}</ref>

Gap junctions were first described as ''close appositions'' alongside tight junctions, however, electron microscopy studies in 1967 led to gap junctions being named as such to be distinguished from tight junctions.<ref>{{cite journal |vauthors=Brightman MW, Reese TS |title=Junctions between intimately apposed cell membranes in the vertebrate brain |date=March 1969 |journal=J. Cell Biol. |volume=40 |issue=3 |pages=648–677 |pmid=5765759 |pmc=2107650 |doi=10.1083/jcb.40.3.648}}</ref> They bridge a 2-4 nm gap between cell membranes.<ref>{{cite journal |last1=Revel |first1=J. P. |last2=Karnovsky |first2=M. J. |title=Hexagonal Array of Subunits in Intercellular Junctions of the Mouse Heart and Liver |journal=Journal of Cell Biology |date=1 June 1967 |volume=33 |issue=3 |pages=C7–12 |doi=10.1083/jcb.33.3.C7|pmid=6036535 |pmc=2107199 }}</ref>

Gap junctions use protein complexes known as [[connexon]]s, composed of [[connexin]] proteins to connect one cell to another. [[Gap junction protein]]s include the more than 26 types of connexin, as well as at least 12 non-connexin components that make up the gap junction complex or ''nexus,''<ref>{{cite journal |last1=Hervé |first1=Jean-Claude |last2=Bourmeyster |first2=Nicolas |last3=Sarrouilhe |first3=Denis |last4=Duffy |first4=Heather S. |title=Gap junctional complexes: From partners to functions |journal=Progress in Biophysics and Molecular Biology |date=May 2007 |volume=94 |issue=1–2 |pages=29–65 |doi=10.1016/j.pbiomolbio.2007.03.010|pmid=17507078 }}</ref> including the [[tight junction protein ZO-1]]—a protein that holds membrane content together and adds structural clarity to a cell,<ref name="Connexin 43 gap junction plaque end">{{cite journal |last1=Gilleron |first1=Jérome |last2=Carette |first2=Diane |last3=Fiorini |first3=Céline |last4=Benkdane |first4=Merieme |last5=Segretain |first5=Dominique |last6=Pointis |first6=Georges |title=Connexin 43 gap junction plaque endocytosis implies molecular remodelling of ZO-1 and c-Src partners |journal=Communicative & Integrative Biology |date=March 2009 |volume=2 |issue=2 |pages=104–106 |doi=10.4161/cib.7626|pmid=19704902 |pmc=2686357 }}</ref> [[sodium channel]]s,<ref name="Localization of Na + channel cluste" /> and [[aquaporin]].<ref>{{cite journal |last1=Yu |first1=Xun Sean |last2=Yin |first2=Xinye |last3=Lafer |first3=Eileen M. |last4=Jiang |first4=Jean X. |title=Developmental Regulation of the Direct Interaction between the Intracellular Loop of Connexin 45.6 and the C Terminus of Major Intrinsic Protein (Aquaporin-0) |journal=Journal of Biological Chemistry |date=June 2005 |volume=280 |issue=23 |pages=22081–22090 |doi=10.1074/jbc.M414377200|doi-access=free |pmid=15802270 }}</ref><ref name="Gruijters, WTM 1989 509–13" />

More gap junction proteins have become known due to the development of [[next-generation sequencing]]. Connexins were found to be structurally homologous between vertebrates and invertebrates but different in sequence.<ref>{{cite journal |last1=Phelan |first1=Pauline |last2=Stebbings |first2=Lucy A. |last3=Baines |first3=Richard A. |last4=Bacon |first4=Jonathan P. |last5=Davies |first5=Jane A. |last6=Ford |first6=Chris |title=Drosophila Shaking-B protein forms gap junctions in paired Xenopus oocytes |journal=Nature |date=January 1998 |volume=391 |issue=6663 |pages=181–184 |doi=10.1038/34426|pmid=9428764 |bibcode=1998Natur.391..181P |s2cid=205003383 }}</ref> As a result, the term [[innexin]] is used to differentiate invertebrate connexins.<ref>{{cite journal |last1=Phelan |first1=Pauline |last2=Bacon |first2=Jonathan P. |last3=A. Davies |first3=Jane |last4=Stebbings |first4=Lucy A. |last5=Todman |first5=Martin G. |title=Innexins: a family of invertebrate gap-junction proteins |journal=Trends in Genetics |date=September 1998 |volume=14 |issue=9 |pages=348–349 |doi=10.1016/s0168-9525(98)01547-9|pmid=9769729 |pmc=4442478 }}</ref> There are more than 20 known innexins,<ref>{{cite journal |last1=Ortiz |first1=Jennifer |last2=Bobkov |first2=Yuriy V |last3=DeBiasse |first3=Melissa B |last4=Mitchell |first4=Dorothy G |last5=Edgar |first5=Allison |last6=Martindale |first6=Mark Q |last7=Moss |first7=Anthony G |last8=Babonis |first8=Leslie S |last9=Ryan |first9=Joseph F |title=Independent Innexin Radiation Shaped Signaling in Ctenophores |journal=Molecular Biology and Evolution |date=3 February 2023 |volume=40 |issue=2 |pages=msad025 |doi=10.1093/molbev/msad025|pmid=36740225 |pmc=9949713 }}</ref> along with unnexins in parasites and [[vinnexin]]s in viruses.

An [[electrical synapse]] is a gap junction that can transmit [[action potential]]s between [[neuron]]s. Such synapses create bidirectional continuous-time electrical coupling<ref name=":0" /><ref name=":1" /> between neurons. Connexon pairs act as generalized regulated gates for ions and smaller molecules between cells. Hemichannel connexons form channels to the extracellular environment.<ref>{{cite journal |last1=Furshpan |first1=E. J. |last2=Potter |first2=D. D. |title=Mechanism of Nerve-Impulse Transmission at a Crayfish Synapse |journal=Nature |date=August 1957 |volume=180 |issue=4581 |pages=342–343 |doi=10.1038/180342a0|pmid=13464833 |bibcode=1957Natur.180..342F |s2cid=4216387 }}</ref><ref name="gj1">{{Cite journal|pmid=15109565 |year=2004 |first1=Paul D. |last1=Lampe |first2=Alan F. |last2=Lau |title=The effects of connexin phosphorylation on gap junctional communication |volume=36 |issue=7 |pages=1171–86 |doi=10.1016/S1357-2725(03)00264-4 |journal=The International Journal of Biochemistry & Cell Biology |pmc=2878204}}</ref><ref name="gj2">{{Cite journal|pmid=11368307 |year=2000 |first1=Paul D. |last1=Lampe |first2=Alan F. |last2=Lau |title=Regulation of gap junctions by phosphorylation of connexins |volume=384 |issue=2 |pages=205–15 |doi=10.1006/abbi.2000.2131 |journal=Archives of Biochemistry and Biophysics}}</ref><ref>{{cite journal |last1=Scemes |first1=Eliana |last2=Spray |first2=David C. |last3=Meda |first3=Paolo |title=Connexins, pannexins, innexins: novel roles of "hemi-channels" |journal=Pflügers Archiv: European Journal of Physiology |date=April 2009 |volume=457 |issue=6 |pages=1207–1226 |doi=10.1007/s00424-008-0591-5|pmid=18853183 |pmc=2656403 }}</ref>

A gap junction or ''macula communicans'' is different from an [[ephaptic coupling]] that involves electrical signals external to the cells.<ref>{{cite journal |last1=Martinez-Banaclocha |first1=Marcos |title=Astroglial Isopotentiality and Calcium-Associated Biomagnetic Field Effects on Cortical Neuronal Coupling |journal=Cells |date=13 February 2020 |volume=9 |issue=2 |pages=439 |doi=10.3390/cells9020439|doi-access=free |pmid=32069981 |pmc=7073214 }}</ref><ref>{{cite journal |last1=Parker |first1=David |title=Neurobiological reduction: From cellular explanations of behavior to interventions |journal=Frontiers in Psychology |date=22 December 2022 |volume=13 |pages=987101 |doi=10.3389/fpsyg.2022.987101|doi-access=free |pmid=36619115 |pmc=9815460 }}</ref>