Free amino acids and cell volume regulation in the elasmobranch, Raja erinacea

Abstract

AbstractFree amino acids comprise a significant fraction of the total intracellular osmolality in skate tissues. The high amino acid concentrations are maintained by active, Na+‐dependent transport systems in the cell membranes. Following transfer to a hypo‐osmotic environment (dilute seawater) cellular concentrations of free amino acids are reduced mainly as a result of increased rates of outflux but decreased rate of influx can also play a role. Metabolism (oxidation and synthesis) does not appear to play a direct role in the modulation of free amino acid concentrations in skeletal muscle cells and erythrocytes. However, continued release of free amino acids from these cells during hypo‐osmotic stress is dependent on the ability of liver and kidney to either oxidize (β‐alanine, sarcosine) or excrete (taurine) amino acids at accelerated rates. A scheme for the overall modulation of cellular free amino acids in skate tissues by a combination of membrane transport, metabolism, and excretion is presented.