Abstract
The metabolic alterations leading to accumulation of amino acids during the initial stages of acclimation to high salinity and anaerobiosis appear to be different in Modiolus demissus demissus. First, the major metabolic event (activation of phosphenolpyruvate carboxykinase) does not appear to occur during acclimation to high salinity since increased incorporation of ^14^C‐bicarbonate into succinate of isolated gills occurred only in anaerobic treatment. Secondly, the cellular changes in concentrations of amino acids and succinate observed in isolated ventricles and gills after exposure to high salinity and anaerobiosis were not similar. Thirdly, during anaerobiosis the total amino‐acid pool remained constant largely because of decreased aspartic acid concentrations.
Although different from the response to anaerobiosis, the mechanism of intracellular free amino acid accumulation during the initial stages of high salinity acclimation also depends on an alteration of intracellular metabolism. Thus, isolated ventricles exposed to salinity increases showed significantly lower levels of radioactivity in glycogen than ventricles maintained in low salinity. Similarly, radioactive glucose was selectively incorporated into the major osmotic solute (alanine) used initially during acclimation to high salinity.
These results suggest that the intracellular free alanine accumulated during acclimation to high salinity is synthesized using glycogen as the carbon source.