KAPPER, M.A.; Central Connecticut State University: Aquaporin and Salinity Adaptation in the Ribbed Mussel

During changes in environmental salinity, osmoconforming estuarine molluscs will initially gain or lose water according to the newly imposed osmotic gradient. Over time the concentration of intracellular organic osmolytes (predominantly free amino acids) will be altered to match the external osmotic concentration. This is associated with a cellular volume regulatory step that brings the cytoplasm back into osmotic equilibrium with the environment. Although the sequence of metabolic events leading to the establishment of a new intracellular solute concentration has been well-described, there has been little attention paid to the mechanism by which water crosses the cell membranes. Since water does not readily cross phospholipid bilayers, cell membranes contain protein channels that are specific for transporting water molecules. Approximately ten members of this aquaporin family have been identified and characterized in organisms as diverse as plants, arthropods and mammals. I hypothesize that during adapatation to increased salinity, the amount of aquaporin-2 in the cell membranes of the ribbed mussel Geukensia demissa gill will be modulated to control water efflux from the cells. To test the hypothesis that membrane water permeability is modulated by the systhesis or destruction of aquaporin, gills from mussels adapted to 15^o/ooS were incubated for up to three hours at 35^o/ooS. Western blots were performed on these tissues along with a parallel set of gills maintained at 15^o/ooS. Following colorimetric development, preliminary data indicate that while aquaporin-2 is indeed present, there is not a significant change in the total amount of aquaporin-2 protein over the course of the three-hour adaptation period. This result suggests a second model, where aquaporin is stored in vesicles that are inserted or removed from the cell membrane as needed to modulate water permeability. Supported in part by a CSU-AAUP faculty research grant to MAK.