HOLT, S.M.; KINSEY, S.T.*: Arginine kinase flux in osmoregulating muscle cells

We examined arginine kinase (AK) flux as a function of intracellular osmogregulatory state in locomotor muscle from blue crab, Callinectes sapidus. Phosphorus nuclear magnetic resonance (NMR) saturation transfer experiments were applied to measure AK flux ex vivo in isolated, superfused swimming leg muscle. Blue crabs were pre-exposed for 7 days to either 5, 17 or 34 ppt salinity prior to experiments. AK flux was then measured using a superfusion medium that had an osmolarity equivalent to that which occurs in blue crabs in vivo at one of the three salinities above (e.g., 5 ppt external salinity = 640 mosM blood). Therefore, we could mimic the osmolarity of the extracellular environment surrounding the muscle cells under physiologically relevant conditions of osmoregulation. AK flux was then measured under condtions of steady-state (superfusion medium = acclimated blood osmolarity), hyperosmotic shock and hyposmotic shock. To further elucidate the role of changes in the intracellular environment on AK function, we also measured AK flux in vitro. Here, we used saturation transfer of isolated AK in solutions comprising different levels of salts and organic osmolytes. Proton NMR was used to help identify the concentrations of the relevant organic osmolytes.