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 Citations (Scopus)

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

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Killifishes
Cyprinodontiformes
Carbonic Anhydrases
Fresh Water
Fish
Ethoxzolamide
Fishes
Protein Isoforms
Thermodynamics
Fluxes
Kinetics
Population

Keywords

  • Carbonic anhydrase
  • Cyprinodon variegatus
  • Ionoregulation
  • Na<sup>+</sup>/H<sup>+</sup> exchange
  • Rh glycoproteins

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Physiology

Cite this

@article{42853f5a9304442aaaf09fda3f046d95,
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 ≥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.",
keywords = "Carbonic anhydrase, Cyprinodon variegatus, Ionoregulation, Na<sup>+</sup>/H<sup>+</sup> exchange, Rh glycoproteins",
author = "Brix, {Kevin V.} and Esbaugh, {Andrew J.} and Mager, {Edward M.} and Martin Grosell",
year = "2015",
month = "7",
day = "1",
doi = "10.1016/j.cbpa.2015.04.002",
language = "English (US)",
volume = "185",
pages = "115--124",
journal = "Comparative Biochemistry & Physiology; A: Comparative Physiology",
issn = "1095-6433",
publisher = "Elsevier Inc.",

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TY - JOUR

T1 - Comparative evaluation of Na+ uptake in Cyprinodon variegatus variegatus (Lacepede) and Cyprinodon variegatus hubbsi (Carr) (Cyprinodontiformes, Teleostei)

T2 - Evaluation of NHE function in high and low Na+ freshwater

AU - Brix, Kevin V.

AU - Esbaugh, Andrew J.

AU - Mager, Edward M.

AU - Grosell, Martin

PY - 2015/7/1

Y1 - 2015/7/1

N2 - 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.

AB - 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.

KW - Carbonic anhydrase

KW - Cyprinodon variegatus

KW - Ionoregulation

KW - Na<sup>+</sup>/H<sup>+</sup> exchange

KW - Rh glycoproteins

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U2 - 10.1016/j.cbpa.2015.04.002

DO - 10.1016/j.cbpa.2015.04.002

M3 - Article

VL - 185

SP - 115

EP - 124

JO - Comparative Biochemistry & Physiology; A: Comparative Physiology

JF - Comparative Biochemistry & Physiology; A: Comparative Physiology

SN - 1095-6433

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