Distinct freshwater and seawater isoforms of Na+/K+-ATPase in gill chloride cells of Atlantic salmon

Abstract

SUMMARYGill 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 1a and 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 1a is slightly less than that for NKA 1b. The abundance of gill NKA 1a was high in freshwater and became nearly undetectable after seawater acclimation. NKA 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 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 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 1a and 1b are located in different chloride cells in freshwater. In many chloride cells in seawater, NKA 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 -subunit in the gills of Atlantic salmon and that they are present in distinct chloride cells.

Switching of Na+, K+-ATPase isoforms by salinity and prolactin in the gill of a cichlid fish

“…Future work should assess whether one or more Fxyd isoforms are co-localized with Na C , K C -ATPase a subunits in tilapia gill. The changes in a-1a and a-1b isoforms observed in tilapia after FW and SW transition in this study largely mirror previous reports in rainbow trout (Richards et al 2003), Arctic char (Bystriansky et al 2006) and Atlantic salmon , McCormick et al 2009). The marked elevation in a-1a expression after FW transition (60-fold) and a-1b expression after SW transition (tenfold) observed in this study is of a greater magnitude than that reported in the salmonid fishes described earlier.…”

“…The discovery of two Na C , K C -ATPase a-1 isoforms in the gill of salmonids, a-1a, expressed mainly in FW, and a-1b, expressed mainly in SW, provided important insight into transepithelial ion transport in the gill. In every salmonid species examined to date, salinity acclimation induces a reciprocal switch between a-1a and a-1b isoforms, a-1a being prominent in FW and a-1b in SW (Richards et al 2003, Mackie et al 2005, Bystriansky et al 2006, McCormick et al 2009), suggesting that a-1a is an FW isoform involved specifically in ion uptake, whereas a-1b is an SW isoform associated with ion excretion. Whether this phenomenon is restricted to the early salmonid branch of the teleost clade or is a more general prerequisite for euryhalinity is unknown.…”

The effects of acute salinity challenges on osmoregulation in Mozambique tilapia reared in a tidally changing salinity

“…NKA provides the driving force for ion transport within ionocytes. In salmon, NKAα1a expression is higher in FW than in SW and NKAα1b expression is higher in SW than in FW (Madsen et al, 2009;McCormick et al, 2009). This pattern of salinity-dependent NKA isoform expression was also described in tilapia .…”

“…The electrochemical gradient that drives transmembrane ion transport is provided by the basolaterally located ion pump, Na + /K + -ATPase (NKA) (Richards et al, 2003). In tilapia, salmonids and killifish, two isoforms of NKA, α1a and α1b, are differentially expressed in the gill, according to the salinity of the habitat (Richards et al, 2003;Madsen et al, 2009;McCormick et al, 2009;Tipsmark et al, 2011;Berdan and Fuller, 2012). In tilapia, NKAα1a expression predominates in FW-acclimated fish relative to SW-acclimated fish, while NKAα1b expression has been shown to be greater or unchanged in SW-acclimated fish when compared with FW-acclimated fish .…”

Changes in gill H+-ATPase and Na+/K+-ATPase expression and activity during freshwater acclimation of Atlantic salmon (Salmo salar)

“…These studies show an increase and then recovery in plasma sodium and chloride levels, coinciding with an increase in gill Na (Hoar, 1988). The observed changes in gill Na + /K + -ATPase expression involve switching between two distinct isoforms of this protein, as mRNA (Richards et al, 2003;Bystriansky et al, 2006) and protein (McCormick et al, 2009) expression of the 1b isoform increases during seawater acclimation, while expression of the 1a isoform decreases during the transition to seawater. In contrast, very few studies have examined the physiology of the gill during acclimation of salmonid fishes to freshwater.…”