epithelial cell ionocyte https://cellxgene.cziscience.com/cellguide/CL_0005006 Specialized epithelial cells involved in the maintenance of osmotic homeostasis. They are characterized by abundant mitochondria and ion transporters. In amniotes, they are present in the renal system. In freshwater fish, ionocytes in the skin and gills help maintain osmotic homeostasis by absorbing salt from the external environment. ZFA:0005323 Ionocytes are specialized cells predominantly found in the mammalian respiratory and renal systems as well as in the gills, skin, and intestinal tract of fish. These cells play crucial roles in maintaining ion and acid-base homeostasis. Ionocytes demonstrate remarkable plasticity and are able to adapt themselves in response to changes in environmental conditions such as pH, salinity, ion concentration, and temperature. These cells work by selectively absorbing specific ions from the environment, thus maintaining the body's internal ionic balance. The most commonly absorbed ions include sodium (Na+), chloride (Cl-), calcium (Ca2+), and hydrogen (H+). Moreover, ionocytes contribute to acid-base regulation. In response to acidosis or alkalosis, ionocytes can either excrete or retain hydrogen (H+) and bicarbonate (HCO3-) ions to readjust the blood pH. Further, experimental evidence suggests a functional complexity of ionocytes, implying diverse roles beyond ion regulation. Recent research highlights ionocytes' involvement in ammonia excretion and the regulation of extracellular fluid volume, highlighting their contribution to the overall homeostatic process. Malfunctioning ionocytes have been implicated in various diseases, including cystic fibrosis which is caused by mutations in the chloride channel CFTR, an ionocyte marker. (This extended description was generated by ChatGPT and reviewed by the CellGuide team, who added references, and by the CL editors, who approved it for inclusion in CL. It may contain information that applies only to some subtypes and species, and so should not be considered definitional.) Homo sapiens