title: Comparative evaluation of Na(+) uptake in Cyprinodon variegatus variegatus (Lacepede) and Cyprinodon variegatus hubbsi (Carr) (Cyprinodontiformes, Teleostei): Evaluation of NHE function in high and low Na(+) freshwater.
abstract: The euryhaline pupfish, Cyprinodon variegatus variegatus (Cvv), can successfully osmoregulate in ≥2 mM Na(+) and a freshwater population (Cyprinodon variegatus hubbsi; Cvh) osmoregulates at ≥0.1mM Na(+). We previously demonstrated that Cvv relies on an apical NKCC and NHE in the gill for Na(+) uptake in high (7mM) and intermediate (2 mM) Na(+) concentrations, while Cvh relies only on NHE for Na(+) uptake. This study investigated whether differential NHE isoform use explains differences in Na(+) uptake kinetics between these two populations. We further studied whether Cvh uses a NHE-Rh metabolon or carbonic anhydrase (CA) to overcome thermodynamic challenges of NHE function in dilute freshwater. Transfer to more dilute freshwater resulted in upregulation of nhe-2 (Cvv only) and nhe-3 (Cvv and Cvh). Relative expression of nhe-3 compared to nhe-2 was 2-fold higher in Cvv, but 200-fold higher in Cvh suggesting that nhe-3 expression is an important freshwater adaptation for Cvh. Simultaneous measurement of Na(+) and Tamm flux under various conditions provided no support for a NHE-Rh metabolon in either population. Carbonic anhydrase activity in Cvv was comparable in 7 and 2 mM Na(+) acclimated fish. In Cvh, CA activity increased by 75% in 0.1 mM Na(+) acclimated fish compared to 7 mM Na(+) fish. Ethoxzolamide had variable effects, stimulating and reducing Na(+) uptake in Cvv acclimated to 7 and 2 mM Na(+), while reducing Na(+) uptake in 7 and 0.1mM Na(+) acclimated Cvh. This suggests that CA plays important, but different roles in regulating Na(+) uptake in Cvv and Cvh.
authors: University of British Columbia, Department of Zoology, 6270 University Drive, Vancouver, British Columbia V6T 1Z4, Canada. Electronic address: brix@zoology.ubc.ca.
authors: Kevin V
authors: KV
authors: Brix
authors: University of Texas, Austin, Marine Science Institute, 750 Channel View Dr., Port Aransas, TX 78373, USA.
authors: Andrew J
authors: AJ
authors: Esbaugh
authors: University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149, USA.
authors: Edward M
authors: EM
authors: Mager
authors: University of Miami, Rosenstiel School of Marine and Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL 33149, USA.
authors: Martin
authors: M
authors: Grosell
mesh_terms: D000064:Acclimatization; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002256:Carbonic Anhydrases / Q000378:metabolism; D029941:Fish Proteins / Q000502:physiology*; D005618:Fresh Water; D015870:Gene Expression; D005880:Gills / Q000378:metabolism; D007695:Killifishes; D000068357:Saline Waters; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology*; D014882:Water-Electrolyte Balance
chemical_list: D029941:Fish Proteins; D017923:Sodium-Hydrogen Exchangers; D000641:Ammonia; D012964:Sodium; D002256:Carbonic Anhydrases
keywords: Carbonic anhydrase; Cyprinodon variegatus; Ionoregulation; Na(+)/H(+) exchange; Rh glycoproteins