P1.54 Wednesday, Jan. 4 IS THE SUBCELLULAR LOCATION OF AQUAPORIN-2 REGULATED BY REVERSIBLE PHOSPHORYLATION DURING SALINITY ADAPTATION IN G. demissa GILL? KAPPER, M.A.; Central Connecticut State University, New Britain email@example.com
Water permeability of cell membranes is predominantly controlled by the presence of aquaporins. When water permeability is changed for physiological reasons, aquaporins will be inserted or removed from the cell membranes. In the collecting duct of the mammalian kidney, aquaporins located in cytosolic vesicles are phosphorylated by a cAMP activated protein kinase when antidiuretic hormone binds to cell surface receptors. These vesicles are then incorporated into the cell membranes, increasing their water permeability. Constitutively active protein phosphatases dephosphorylate the aquaporins, initiating their removal from the cell membranes. It is well known that osmoconforming marine invertebrates lessen or eliminate the osmotic gradient imposed by the changing tides by modulating the concentration of intracellular organic osmolytes, primarily free amino acids. Before this regulatory step is completed, there is a transient change in cell volume due to osmotic movement of water across the cell membranes. We are testing the hypothesis that water permeability in gill epithelia of the ribbed mussel Geukensia demissa is modulated by removing aquaporins from the cell membranes during the initial stages of salinity adaptation. Immunofluorescence microscopy suggests that aquaporin proteins are removed from the cell membrane after transfer from low to high salinity. Western blotting and immunoprecipitation indicate that both phosphorylated and unphosphorylated forms of aquaporin-2 are present in G. demissa gill. We are currently determining whether the amount of unphosphorylated aquaporin increases during the initial stages of salinity adaptation. Supported by a CSU/AAUP Faculty Research Grant to MAK.