title: Does Japanese medaka (Oryzias latipes) exhibit a gill Na(+)/K(+)-ATPase isoform switch during salinity change?
abstract: Some euryhaline teleosts exhibit a switch in gill Na(+)/K(+)-ATPase (Nka) α isoform when moving between fresh water (FW) and seawater (SW). The present study tested the hypothesis that a similar mechanism is present in Japanese medaka and whether salinity affects ouabain, Mg(2+), Na(+) and K(+) affinity of the gill enzyme. Phylogenetic analysis classified six separate medaka Nka α isoforms (α1a, α1b, α1c, α2, α3a and α3b). Medaka acclimated long-term (>30 days) to either FW or SW had similar gill expression of α1c, α2, α3a and α3b, while both α1a and α1b were elevated in SW. Since a potential isoform shift may rely on early changes in transcript abundance, we conducted two short-term (1-3 days) salinity transfer experiments. FW to SW acclimation induced an elevation of α1b and α1a after 1 and 3 days. SW to FW acclimation reduced α1b after 3 days with no other α isoforms affected. To verify that the responses were typical, additional transport proteins were examined. Gill ncc and nhe3 expression were elevated in FW, while cftr and nkcc1a were up-regulated in SW. This is in accordance with putative roles in ion-uptake and secretion. SW-acclimated medaka had higher gill Nka V max and lower apparent K m for Na(+) compared to FW fish, while apparent affinities for K(+), Mg(2+) and ouabain were unchanged. The present study showed that the Japanese medaka does not exhibit a salinity-induced α isoform switch and therefore suggests that Na(+) affinity changes involve altered posttranslational modification or intermolecular interactions.
authors.affiliation: Department of Biological Sciences, University of Arkansas, SCEN 601, Fayetteville, AR, 72701, USA.
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Bollinger
authors.affiliation: Department of Biological Sciences, University of Arkansas, SCEN 601, Fayetteville, AR, 72701, USA.|Department of Biology, University of Southern Denmark, Campusvej 55, 5230, Odense M, Denmark.
authors.forename: Steffen S
authors.initials: SS
authors.lastname: Madsen
authors.affiliation: Department of Biological Sciences, University of Arkansas, SCEN 601, Fayetteville, AR, 72701, USA.
authors.forename: Maryline C
authors.initials: MC
authors.lastname: Bossus
authors.affiliation: Department of Biological Sciences, University of Arkansas, SCEN 601, Fayetteville, AR, 72701, USA. tipsmark@uark.edu.
authors.forename: Christian K
authors.initials: CK
authors.lastname: Tipsmark
mesh_terms: D000064:Acclimatization; D000818:Animals; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D005880:Gills / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D009990:Oryzias / Q000378:metabolism / Q000502:physiology*; D010042:Ouabain / Q000378:metabolism; D010802:Phylogeny; D011188:Potassium / Q000378:metabolism; D054712:Salinity; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
chemical_list: D029941:Fish Proteins; D007527:Isoenzymes; D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium
keywords: Euryhaline teleost; Na+/K+-ATPase enzymatic activity; Osmoregulation; Substrate affinity; α-Subunit