Comparative evaluation of Na<sup>+</sup> uptake in Cyprinodon variegatus variegatus (Lacepede) and Cyprinodon variegatus hubbsi (Carr) (Cyprinodontiformes, Teleostei): Evaluation of NHE function in high and low Na<sup>+</sup> freshwater

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

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

The euryhaline pupfish, Cyprinodon variegatus variegatus (Cvv), can successfully osmoregulate in ≥2mM Na<sup>+</sup> and a freshwater population (Cyprinodon variegatus hubbsi; Cvh) osmoregulates at ≥0.1mM Na<sup>+</sup>. We previously demonstrated that Cvv relies on an apical NKCC and NHE in the gill for Na<sup>+</sup> uptake in high (7mM) and intermediate (2mM) Na<sup>+</sup> concentrations, while Cvh relies only on NHE for Na<sup>+</sup> uptake. This study investigated whether differential NHE isoform use explains differences in Na<sup>+</sup> 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<sup>+</sup> and T<inf>amm</inf> 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<sup>+</sup> acclimated fish. In Cvh, CA activity increased by 75% in 0.1mM Na<sup>+</sup> acclimated fish compared to 7mM Na<sup>+</sup> fish. Ethoxzolamide had variable effects, stimulating and reducing Na<sup>+</sup> uptake in Cvv acclimated to 7 and 2mM Na<sup>+</sup>, while reducing Na<sup>+</sup> uptake in 7 and 0.1mM Na<sup>+</sup> acclimated Cvh. This suggests that CA plays important, but different roles in regulating Na<sup>+</sup> 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<sup>+</sup>/H<sup>+</sup> exchange
  • Rh glycoproteins

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Physiology

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