title: Characterization of developmental Na(+) uptake in rainbow trout larvae supports a significant role for Nhe3b.
abstract: Developing freshwater fish must compensate for the loss of ions, including sodium (Na(+)), to the environment. In this study, we used a radiotracer flux approach and pharmacological inhibitors to investigate the role of sodium/hydrogen exchange proteins (Nhe) in Na(+) uptake in rainbow trout (Oncorhynchus mykiss) reared from fertilization in soft water (0.1mM Na(+)). For comparison, a second group of embryos/larvae reared in hard water (2.2mM Na(+), higher pH and [Ca(2+)]) were also included in the experiment but were fluxed in soft water, only. Unidirectional rates of Na(+) uptake increased throughout development and were significantly higher in embryos/larvae reared in soft water. However, the mechanisms of Na(+) uptake in both groups of larvae were not significantly different, either in larvae immediately post-hatch or later in development: the broad spectrum Na(+) channel blocker amiloride inhibited 85-90% of uptake and the Nhe-inhibitor EIPA also caused near maximal inhibitions of Na(+) uptake. These data indicated Na(+) uptake was Nhe-mediated in soft water. A role of Nhe3b (but not Nhe2 or Nhe3a) in Na(+) uptake in soft water was also supported through gene expression analyses: expression of nhe3b increased throughout development in whole embryos/larvae in both groups and was significantly higher in those reared in soft water. This pattern of expression correlated well with measurements of Na(+) uptake. Together these data indicate that in part, rainbow trout embryos/larvae reared in low Na(+) soft water maintained Na(+) homeostasis by an EIPA sensitive component of Na(+) uptake, and support a primary role for Nhe3b.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Boyle
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
authors.forename: Salvatore D
authors.initials: SD
authors.lastname: Blair
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
authors.forename: Danuta
authors.initials: D
authors.lastname: Chamot
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada. Electronic address: greg.goss@ualberta.ca.
authors.forename: Greg G
authors.initials: GG
authors.lastname: Goss
mesh_terms: D000818:Animals; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D017136:Ion Transport; D007814:Larva / Q000378:metabolism; D017686:Oncorhynchus mykiss / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D029941:Fish Proteins; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium
keywords: Acid-base balance; Embryo; Ionoregulation; Rainbow trout; Sodium