Gill Na+-K+-2Cl(-) cotransporter abundance and location in Atlantic salmon: effects of seawater and smolting

Na+-K+-2Cl(-) cotransporter abundance and location was examined in the gill s of Atlantic salmon (Salmo salar) during seawater acclimation and smolting . Western blots revealed three bands centered at 285, 160, and 120 kDa. The Na+-K+-2Cl(-) cotransporter was colocalized with Na+-K+-ATPase to chloride cells on both the primary filament and secondary lamellae. Parr acclimated to 30 parts per thousand seawater had increased gill Na+-K+-2Cl(-) cotrans porter abundance, large and numerous Na+-K+-2Cl(-) cotransporter immunoreac tive chloride cells on the primary filament, and reduced numbers on the sec ondary lamellae. Gill Na+-K+-2Cl(-) cotransporter levels were low in presmo lts (February) and increased 3.3-fold in smolts (May), coincident with elev ated seawater tolerance. Cotransporter levels decreased below presmolt valu es in postsmolts in freshwater (June). The size and number of immunoreactiv e chloride cells on the primary filament increased threefold during smoltin g and decreased in postsmolts. Gill Na+-K+-ATPase activity and Na+-K+-2Cl(- ) cotransporter abundance increased in parallel during both seawater acclim ation and smolting. These data indicate a direct role of the Na+-K+-2Cl(-) cotransporter in salt secretion by gill chloride cells of teleost fish.