Piermarini, P.M.*; Evans, D.H.: Effect of salinity on expression of the vacuolar proton-ATPase B-subunit in the gills of a euryhaline stingray (Dasyatis sabina)

The vacuolar proton-ATPase (V-H-ATPase) is an important ion transporter that is responsible for energizing a variety of active transport processes in animals. Recently, the V-H-ATPase has been considered alikely transporter for driving active sodium uptake by the gills of freshwater teleosts. In addition, it has been demonstrated that the activity and expression of V-H-ATPase in the gills decreased when freshwater rainbow trout (Oncorhynchus mykiss), were acclimated to seawater. To date, V-H-ATPase has been immunolocalized in the gills of a marine elasmobranch (Squalus acanthias), but studies on its expression in response to changes in environmental salinity have yet to be conducted. In this study, we used immunochemical techniques to examine the effect of environmental salinity on expression of the V-H-ATPase B-subunit in a euryhaline elasmobranch, the Atlantic stingray (Dasyatis sabina). Western blots demonstrated that V-H-ATPase expression was negatively correlated with environmental salinity; gills from freshwater rays demonstrated the highest abundance of the transporter, while lowest abundance was associated with gills from seawater rays. Immunohistochemistry revealed that V-H-ATPase-rich cells were present on both the gill lamellae and interlamellar region of freshwater rays, while seawater rays only had V-H-ATPase-rich cells on the gill interlamellar region. Our results demonstrate that branchial V-H-ATPase expression in the Atlantic stingray follows a similar trend as found in the rainbow trout, and we suggest that the V-H-ATPase in elasmobranch gills may be important for ion uptake from freshwater environments. Supported by EPA STAR Grant U-915419-01-0 (PMP) and NSF Grant IBN-9604824 (DHE).