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First published online November 27, 2009
Journal of Experimental Biology 212, 3994-4001 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.037275
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Distinct freshwater and seawater isoforms of Na+/K+-ATPase in gill chloride cells of Atlantic salmon

S. D. McCormick*, A. M. Regish and A. K. Christensen

USGS, Conte Anadromous Fish Research Center, Turners Falls, MA, USA and Department of Biology, University of Massachusetts, Amherst, MA 01003, USA

* Author for correspondence (mccormick{at}umext.umass.edu)

Accepted 28 September 2009

Gill Na+/K+-ATPase (NKA) in teleost fishes is involved in ion regulation in both freshwater and seawater. We have developed and validated rabbit polyclonal antibodies specific to the NKA {alpha}1a and {alpha}1b protein isoforms of Atlantic salmon (Salmo salar Linnaeus), and used western blots and immunohistochemistry to characterize their size, abundance and localization. The relative molecular mass of NKA {alpha}1a is slightly less than that for NKA β1b. The abundance of gill NKA {alpha}1a was high in freshwater and became nearly undetectable after seawater acclimation. NKA {alpha}1b was present in small amounts in freshwater and increased 13-fold after seawater acclimation. Both NKA isoforms were detected only in chloride cells. NKA {alpha}1a was located in both filamental and lamellar chloride cells in freshwater, whereas in seawater it was present only as a faint background in filamental chloride cells. In freshwater, NKA {alpha}1b was found in a small number of filamental chloride cells, and after seawater acclimation it was found in all chloride cells on the filament and lamellae. Double simultaneous immunofluorescence indicated that NKA {alpha}1a and {alpha}1b are located in different chloride cells in freshwater. In many chloride cells in seawater, NKA {alpha}1b was present in greater amounts in the subapical region than elsewhere in the cell. The combined patterns in abundance and immunolocalization of these two isoforms can explain the salinity-related changes in total NKA and chloride cell abundance. The results indicate that there is a freshwater and a seawater isoform of NKA {alpha}-subunit in the gills of Atlantic salmon and that they are present in distinct chloride cells.

Key words: osmoregulation, ion transport, mitochondrion-rich cell, Salmo salar


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