Abstract
AbstractDuring adaptation to low salinity (from 20 to 2 ppt), the estuarine clam Rangia cuneata reduces the size of a pool of free amino acids in adductor muscle fibers, presumably to control cell volume. The levels of both free amino acids and ammonia in the blood increase, but the rise in free amino acids is much greater. While free amino acid excretion is never very great, ammonia excretion rises shortly after valve opening and remains high throughout the period of adaptation Evaluation of the convection capability of the cardiovascular system suggests that the rate of free amino acid excretion cannot explain the loss of these substances as such from the tissues. Conversely, the levels of ammonia in blood cannot explain the rate of excretion. We suggest that most of the free amino acids are extruded from the cells and transported to a central site of deamination, from which ammonia is excreted. In situ deamination in the various tissues may occur after the initial stages of low salinity adjustment, but it never appears to explain the major fraction of ammonia excretion.
Published Version
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