Effects of environmental salinity on Na+/K+-ATPase in the gills and rectalgland of a euryhaline elasmobranch (Dasyatis sabina)

Changes in Na+/K+-ATPase activity and abundance associated with environment al salinity were investigated in the gills and rectal gland of the Atlantic stingray Dasyatis sabina, Using a ouabain-specific ATPase assay and wester n blotting, we found that stingrays from fresh water had the highest activi ty and highest relative abundance of Na+/K+-ATPase in the gills. Using immu nohistochemistry, we also found that gills from freshwater stingrays had th e greatest number of Na+/K+-ATPase-rich cells, When freshwater stingrays we re acclimated to sea mater for 1 week, the activity and abundance of Na+/K-ATPase and the number of Na+/K+-ATPase-rich cells decreased in the gills. In seawater stingrays, the branchial activity and abundance of Na+/K+-ATPas e and the number of Na+/K+-ATPase-rich cells were further reduced. In recta l glands, the activity and abundance of Na+/K+-ATPase were lower in freshwa ter animals than in seawater-acclimated and seawater stingrays, both of whi ch had equivalent levels. These findings suggest that salinity-associated c hanges in gill and rectal gland Na+/K+-ATPase activity are due to changes i n the abundance of Na+/K+-ATPase. We conclude that the gills may be importa nt for active ion uptake in fresh water, while the rectal gland is importan t for active NaCl excretion in sea water. The results from this study are t he first to demonstrate an effect of environmental salinity on Na+/K+-ATPas e expression in the gills and rectal gland of an elasmobranch.