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

Kevin V. Brix, Andrew J. Esbaugh, Edward M. Mager, Martin Grosell

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

The euryhaline pupfish, Cyprinodon variegatus variegatus (Cvv), can successfully osmoregulate in ≥2mM 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 (2mM) 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 2mM Na+ acclimated fish. In Cvh, CA activity increased by 75% in 0.1mM Na+ acclimated fish compared to 7mM Na+ fish. Ethoxzolamide had variable effects, stimulating and reducing Na+ uptake in Cvv acclimated to 7 and 2mM 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.

Original languageEnglish (US)
Pages (from-to)115-124
Number of pages10
JournalComparative Biochemistry and Physiology -Part A : Molecular and Integrative Physiology
Volume185
DOIs
StatePublished - Jul 1 2015

Keywords

  • Carbonic anhydrase
  • Cyprinodon variegatus
  • Ionoregulation
  • Na/H exchange
  • Rh glycoproteins

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Molecular Biology

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