{{Short description|Mitochondria rich cell in animals}} thumb| {{center|Microscopic image of two ionocytes in a gill}}
An '''ionocyte''' (formerly called a chloride cell) is a mitochondrion-rich cell within ionoregulatory organs of animals, such as teleost fish gill, insect Malpighian tubules, crustacean gills, antennal glands and maxillary glands, and copepod Crusalis organs.<ref name="Gerber_2016">{{cite journal | doi=10.1086/686323 | title=The Legs Have It: In Situ Expression of Ion Transporters V-Type H<sup>+</sup>-ATPase and Na<sup>+</sup>/K<sup>+</sup>-ATPase in the Osmoregulatory Leg Organs of the Invading Copepod ''Eurytemora affinis'' | date=2016 | last1=Gerber | first1=Lucie | last2=Lee | first2=Carol Eunmi | last3=Grousset | first3=Evelyse | last4=Blondeau-Bidet | first4=Eva | last5=Boucheker | first5=Nesrine Boudour | last6=Lorin-Nebel | first6=Catherine | last7=Charmantier-Daures | first7=Mireille | last8=Charmantier | first8=Guy | journal=Physiological and Biochemical Zoology | volume=89 | issue=3 | pages=233–250 | pmid=27153133 }}</ref> These cells contribute to the maintenance of optimal osmotic, ionic, and acid-base levels within metazoans. In aquatic invertebrates, ionocytes perform the functions of both ion uptake and ion excretion.<ref>{{cite journal | vauthors = Charmantier G, Charmantier-Daures M, Towle D| title = Osmotic and ionic regulation in aquatic arthropods | journal = Osmotic and Ionic Regulation | pages = 165–230}}</ref> In marine teleost fish, by expending energy to power the enzyme Na<sup>+</sup>/K<sup>+</sup>-ATPase and in coordination with other protein transporters, ionocytes pump excessive sodium and chloride ions against the concentration gradient into the ocean.<ref name="Evans_2005">{{cite journal | vauthors = Evans DH, Piermarini PM, Choe KP | title = The multifunctional fish gill: dominant site of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste | journal = Physiological Reviews | volume = 85 | issue = 1 | pages = 97–177 | date = January 2005 | pmid = 15618479 | doi = 10.1152/physrev.00050.2003 }}</ref><ref>{{cite journal | vauthors = Marshall WS | title = Na(+), Cl(-), Ca(2+) and Zn(2+) transport by fish gills: retrospective review and prospective synthesis | journal = The Journal of Experimental Zoology | volume = 293 | issue = 3 | pages = 264–83 | date = August 2002 | pmid = 12115901 | doi = 10.1002/jez.10127 }}</ref><ref name="Hirose_2003">{{cite journal | vauthors = Hirose S, Kaneko T, Naito N, Takei Y | title = Molecular biology of major components of chloride cells | journal = Comparative Biochemistry and Physiology. Part B, Biochemistry & Molecular Biology | volume = 136 | issue = 4 | pages = 593–620 | date = December 2003 | pmid = 14662288 | doi = 10.1016/s1096-4959(03)00287-2 }}</ref> Conversely, freshwater teleost ionocytes use this low intracellular environment to attain sodium and chloride ions into the organism, and also against the concentration gradient.<ref name="Evans_2005" /><ref name="Hirose_2003" /> In larval fishes with underdeveloped / developing gills, ionocytes can be found on the skin and fins.<ref>{{cite journal | vauthors = Glover CN, Bucking C, Wood CM | title = The skin of fish as a transport epithelium: a review | journal = Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology | volume = 183 | issue = 7 | pages = 877–91 | date = October 2013 | pmid = 23660826 | doi = 10.1007/s00360-013-0761-4 | s2cid = 17089043 }}</ref><ref>{{cite journal | vauthors = Kwan GT, Wexler JB, Wegner NC, Tresguerres M | title = Ontogenetic changes in cutaneous and branchial ionocytes and morphology in yellowfin tuna (Thunnus albacares) larvae | journal = Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology | volume = 189 | issue = 1 | pages = 81–95 | date = February 2019 | pmid = 30357584 | doi = 10.1007/s00360-018-1187-9 | s2cid = 53025702 | url = https://escholarship.org/uc/item/9hn1c0qn }}</ref><ref>{{cite journal | vauthors = Varsamos S, Nebel C, Charmantier G | title = Ontogeny of osmoregulation in postembryonic fish: a review | journal = Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology | volume = 141 | issue = 4 | pages = 401–29 | date = August 2005 | pmid = 16140237 | doi = 10.1016/j.cbpb.2005.01.013 }}</ref>
==Mechanism of action== Marine teleost fishes consume large quantities of seawater to reduce osmotic dehydration.<ref name="dict">{{cite web | url =http://www.encyclopedia.com/doc/1O8-chloridecells.html |title=Chloride cells|work=A Dictionary of Zoology| first = Michael | last = Allaby | name-list-style = vanc | access-date =4 July 2015}}</ref> The excess of ions absorbed from seawater is pumped out of the teleost fishes via the ionocytes.<ref name="dict"/> These cells use active transport on the basolateral (internal) surface to accumulate chloride, which then diffuses out of the apical (external) surface and into the surrounding environment.<ref name="Wilmer_2005">{{Cite book|title = Environmental Physiology of Animals|last1 = Wilmer|first1 = Pat|last2 = Stone|first2 = Graham|last3 = Johnston|first3 = Ian | name-list-style = vanc |publisher = Blackwell|year = 2005|isbn = 978-1-4051-0724-2|location = Malden, MA|pages = [https://archive.org/details/environmentalphy00will/page/85 85]|url-access = registration|url = https://archive.org/details/environmentalphy00will/page/85}}</ref> Such mitochondrion-rich cells are found in both the gill lamellae and filaments of teleost fish. Using a similar mechanism, freshwater teleost fish use these cells to take in salt from their dilute environment to prevent hyponatremia from water diffusing into the fish.<ref name="Wilmer_2005" /> In the context of freshwater fish, ionocytes are often referred to as "mitochondria-rich cells", to emphasis their high density of mitochondria.<ref>Fernandes, M.N. (2019) "Respiration and Ionic-Osmoregulation". In: Formicki K and Kirschbaum F (Eds.) ''The Histology of Fishes'' pages 246–266, CRC Press. {{ISBN|9781498784481}}.</ref>
==See also== * Pulmonary ionocyte - a rare type of specialised cell that may regulate mucus viscosity in humans
== References == {{reflist|30em}}
== Further reading == {{refbegin}} * {{cite journal | vauthors = Zadunaisky JA | title = Chloride cells and osmoregulation | journal = Kidney International | volume = 49 | issue = 6 | pages = 1563–7 | date = June 1996 | pmid = 8743455 | doi = 10.1038/ki.1996.225 | doi-access = free }} {{refend}}
Category:Cells Category:Fish anatomy
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