Effects of growth hormone and cortisol on Na+-K+-2C1-cotransporter localization and abundance the gills of Atlantic salmon

The hormones responsible for the regulation of the teleostean gill Na⁺–K⁺–2Cl⁻ cotransporter have not been elucidated. With Western blotting and immunocytochemistry, Na⁺–K⁺–2Cl⁻ cotransporter abundance and localization were examined in the gills of Atlantic salmon (Salmo salar) following 2-week treatment with growth hormone (GH; 5.0 μg · g⁻¹), cortisol (50 μg · g⁻¹), and both hormones in combination (GH+cortisol). GH and cortisol treatments increased gill Na⁺–K⁺–2Cl⁻ cotransporter abundance over levels seen in controls, and both hormones together (GH+cortisol) produced a greater effect than either hormone alone. Gill Na⁺,K⁺–ATPase activity was also elevated by all three hormone treatments. Compared to controls, Na⁺–K⁺–2Cl⁻ cotransporter immunoreactive chloride cells on the primary filament were greater in number and size following all three treatments. Although the number of immunoreactive chloride cells on the secondary lamellae did not differ among the treatment groups, GH+cortisol increased their size. These data indicate that GH and cortisol increase gill Na⁺–K⁺–2Cl⁻ cotransporter abundance through chloride cell proliferation and differentiation in the gills of Atlantic salmon and are likely the hormones responsible for Na⁺–K⁺–2Cl⁻ cotransporter regulation during smolting and seawater acclimation.