The mechanism of crustacean salinity tolerance: Cell volume regulation by K+ and glycine effluxes

The regulation of muscle fiber K⁺ and free amino acid (FAA) concentrations during hypoosmotic stress was investigated in the moderately euryhaline crab Cancer irroratus. After 6 h of exposure to 60% ASW, muscle fiber K⁺ concentration declined from 185 mM to 140 mM. Following this, the blood glycine levels began to increase, indicating an FAA efflux from the cells. These data indicate that both muscle fiber K⁺ and FAA contribute to cell volume regulation in C. irroratus. The early release of K⁺ limits the initial rate of cell hydration. The subsequent efflux of glycine accounts for the volume regulation response of the muscle fibers. The cell volume regulatory system of C. irroratus is a coordinated use of both inorganic ions and FAA.