Ionocyte Explained

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.^[1] 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.^[2] In marine teleost fish, by expending energy to power the enzyme Na⁺/K⁺-ATPase and in coordination with other protein transporters, ionocytes pump excessive sodium and chloride ions against the concentration gradient into the ocean.^{[3] [4] [5]} Conversely, freshwater teleost ionocytes use this low intracellular environment to attain sodium and chloride ions into the organism, and also against the concentration gradient. In larval fishes with underdeveloped / developing gills, ionocytes can be found on the skin and fins.^{[6] [7] [8]}

Mechanism of action

Marine teleost fishes consume large quantities of seawater to reduce osmotic dehydration.^[9] The excess of ions absorbed from seawater is pumped out of the teleost fishes via the ionocytes.^[9] 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.^[10] 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. In the context of freshwater fish, ionocytes are often referred to as "mitochondria-rich cells", to emphasis their high density of mitochondria.^[11]

See also

• Pulmonary ionocyte - a rare type of specialised cell that may regulate mucus viscosity in humans

Further reading

• Zadunaisky JA . Chloride cells and osmoregulation . Kidney International . 49 . 6 . 1563–7 . June 1996 . 8743455 . 10.1038/ki.1996.225 . free .

Notes and References

1. Gerber L, Lee CE, Grousset E, Blondeau-Bidet E, Boucheker NB, Lorin-Nebel C, Charmantier-Daures M, Charmantier G . The Legs Have It: In situ expression of ion transporters V-Type H+ ATPase and Na+/K+-ATPase in osmoregulating leg organs of the invading copepod Eurytemora affinis . Physiological and Biochemical Zoology . 89 . 3 . 233-250 . 2016 . 10.1152/physrev.00050.200310.1086/686323 .
2. Charmantier G, Charmantier-Daures M, Towle D. Osmotic and ionic regulation in aquatic arthropods . Osmotic and Ionic Regulation . 165-230.
3. Evans DH, Piermarini PM, Choe KP . The multifunctional fish gill: dominant site of gas exchange, osmoregulation, acid-base regulation, and excretion of nitrogenous waste . Physiological Reviews . 85 . 1 . 97–177 . January 2005 . 15618479 . 10.1152/physrev.00050.2003 .
4. Marshall WS . Na(+), Cl(-), Ca(2+) and Zn(2+) transport by fish gills: retrospective review and prospective synthesis . The Journal of Experimental Zoology . 293 . 3 . 264–83 . August 2002 . 12115901 . 10.1002/jez.10127 .
5. Hirose S, Kaneko T, Naito N, Takei Y . Molecular biology of major components of chloride cells . Comparative Biochemistry and Physiology. Part B, Biochemistry & Molecular Biology . 136 . 4 . 593–620 . December 2003 . 14662288 . 10.1016/s1096-4959(03)00287-2 .
6. Glover CN, Bucking C, Wood CM . The skin of fish as a transport epithelium: a review . Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology . 183 . 7 . 877–91 . October 2013 . 23660826 . 10.1007/s00360-013-0761-4 . 17089043 .
7. Kwan GT, Wexler JB, Wegner NC, Tresguerres M . Ontogenetic changes in cutaneous and branchial ionocytes and morphology in yellowfin tuna (Thunnus albacares) larvae . Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology . 189 . 1 . 81–95 . February 2019 . 30357584 . 10.1007/s00360-018-1187-9 . 53025702 .
8. Varsamos S, Nebel C, Charmantier G . Ontogeny of osmoregulation in postembryonic fish: a review . Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology . 141 . 4 . 401–29 . August 2005 . 16140237 . 10.1016/j.cbpb.2005.01.013 .
9. Web site: Chloride cells. A Dictionary of Zoology. Michael . Allaby . vanc . 4 July 2015.
10. Book: Environmental Physiology of Animals. Wilmer. Pat. Stone. Graham. Johnston. Ian . vanc . Blackwell. 2005. 978-1-4051-0724-2. Malden, MA. 85. registration.
11. Fernandes, M.N. (2019) "Respiration and Ionic-Osmoregulation". In: Formicki K and Kirschbaum F (Eds.) The Histology of Fishes pages 246–266, CRC Press. .