A mechanism for branchial acid excretion in marine fish: Identification of multiple Na+/H+ antiporter (NHE) isoforms in gills of two seawater teleosts

J. B. Claiborne, C. R. Blackston, K. P. Choe, D. C. Dawson, S. P. Harris, L. A. Mackenzie, A. I. Morrison-Shetlar

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70 Scopus citations

Abstract

Both Na+/H+ exchange and the electrogenic extrusion of H+ via an H+-ATPase have been postulated to drive acid excretion across the branchial epithelium of fishes. While the H+-ATPase/Na+ channel system appears to be the predominant mechanism in some freshwater species, it may play a reduced role in seawater and brackish-water animals, where high external Na+ concentrations may thermodynamically favor Na+/H+ exchange driven by a Na+/H+ antiporter (NHE). In this study, we used molecular and immunological methods to assess the role of NHE isoforms in the branchial epithelium of the marine long-horned sculpin (Myoxocephalus octodecimspinosus) and the euryhaline killifish (Fundulus heteroclitus). Northern blot analysis of RNA probed with the human NHE-1 BamHI fragment suggested the presence of homologous gill NHE mRNA in sculpin. RT-PCR on gill RNA isolated from sculpin recovering from metabolic acidosis provided evidence for two distinct NHE isoforms; one with 76% amino acid homology to mammalian NHE-2, and another 92% homologous to trout erythrocytic β-NHE. Killifish also have transcripts with 91% homology to β-NHE. Immunological detection using monoclonal antibodies for mammalian NHE-1 revealed a protein antigenically similar to this isoform in the gills of both species. Metabolic acidosis caused an approximately 30-fold decrease in expression of the NHE-1-like protein in sculpin. We speculate that β-NHE in the gills plays the intracellular 'housekeeping' roles described for mammalian NHE-1. During systemic acidosis, apical gill NHE-2 (which is sensitive to external amiloride and low [Na+]) in parallel with a dramatic suppression of basolateral NHE-1 activity enhances net AH+ transfers to the water.

Original languageEnglish (US)
Pages (from-to)315-324
Number of pages10
JournalJournal of Experimental Biology
Volume202
Issue number3
StatePublished - Feb 1 1999

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Keywords

  • Acid-base
  • Euryhaline
  • Fundulus heteroclitus
  • Gill
  • H excretion
  • Killifish
  • Myoxocephalus octodecimspinosus
  • PH balance
  • Salinity
  • Sculpin
  • Stenohaline

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science

Cite this

Claiborne, J. B., Blackston, C. R., Choe, K. P., Dawson, D. C., Harris, S. P., Mackenzie, L. A., & Morrison-Shetlar, A. I. (1999). A mechanism for branchial acid excretion in marine fish: Identification of multiple Na+/H+ antiporter (NHE) isoforms in gills of two seawater teleosts. Journal of Experimental Biology, 202(3), 315-324.