title: Gene expression and cellular localization of ROMKs in the gills and kidney of Mozambique tilapia acclimated to fresh water with high potassium concentration.
abstract: Regulation of plasma K(+) levels in narrow ranges is vital to vertebrate animals. Since seawater (SW) teleosts are loaded with excess K(+), they constantly excrete K(+) from the gills. However, the K(+) regulatory mechanisms in freshwater (FW)-acclimated teleosts are still unclear. We aimed to identify the possible K(+) regulatory mechanisms in the gills and kidney, the two major osmoregulatory organs, of FW-acclimated Mozambique tilapia (Oreochromis mossambicus). As a potential molecular candidate for renal K(+) handling, a putative renal outer medullary K(+) channel (ROMK) was cloned from the tilapia kidney and tentatively named "ROMKb"; another ROMK previously cloned from the tilapia gills was thus renamed "ROMKa". The fish were acclimated to control FW or to high-K(+) (H-K) FW for 1 wk, and we assessed physiological responses of tilapia to H-K treatment. As a result, urinary K(+) levels were slightly higher in H-K fish, implying a role of the kidney in K(+) excretion. However, the mRNA expression levels of both ROMKa and ROMKb were very low in the kidney, while that of K(+)/Cl(-) cotransporter 1 (KCC1) was robust. In the gills, ROMKa mRNA was markedly upregulated in H-K fish. Immunofluorescence staining showed that branchial ROMKa was expressed at the apical membrane of type I and type III ionocytes, and the ROMKa immunosignals were more intense in H-K fish than in control fish. The present study suggests that branchial ROMKa takes a central role for K(+) regulation in FW conditions and that K(+) excretion via the gills is activated irrespective of environmental salinity.
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, Japan; and fumiya@marine.fs.a.u-tokyo.ac.jp.
authors.forename: Fumiya
authors.initials: F
authors.lastname: Furukawa
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, Japan; and.
authors.forename: Soichi
authors.initials: S
authors.lastname: Watanabe
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, Japan; and.
authors.forename: Keigo
authors.initials: K
authors.lastname: Kakumura
authors.affiliation: Department of Anatomy, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan.
authors.forename: Junya
authors.initials: J
authors.lastname: Hiroi
authors.affiliation: Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo, Japan; and.
authors.forename: Toyoji
authors.initials: T
authors.lastname: Kaneko
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D005618:Fresh Water; D015870:Gene Expression / Q000502:physiology*; D005880:Gills / Q000166:cytology / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D024661:Potassium Channels, Inwardly Rectifying / Q000096:biosynthesis / Q000235:genetics*; D064507:Solute Carrier Family 12, Member 4 / Q000378:metabolism; D017210:Tilapia / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000235:genetics / Q000502:physiology
chemical_list: D024661:Potassium Channels, Inwardly Rectifying; D064507:Solute Carrier Family 12, Member 4; D011188:Potassium
keywords: Kir1.1; Oreochromis mossambicus; freshwater adaptation; osmoregulation; potassium