INTRACELLULAR OSMOREGULATION IN SKELETAL MUSCLE DURING SALINITY ADAPTATION IN TWO SPECIES OF TOADS

Abstract

A detailed study of intracellular osmoregulation in skeletal muscles has been carried out in 2 species of toads, Bufo viridis and Bufo boreas, adapted to various salinities between freshwater and 50% sea water (salinity 16%o). Both species are osmo-conformers, changes in plasma osmotic concentrations are due almost entirely to changes in NaCl concentrations. Muscle dry weight, however, is more stable, increasing by less than 35% in both forms in the face of plasma osmotic concentration increases of 80-135%. Muscle extracellular volume (inulin space) is constant, independent of changes in plasma concentration. Relative stability of muscle hydra-tion is due to accumulation of intracellular solutes. Changes in intracellular osmotic concentration are broadly partitioned 47% inorganic ions (Cl, Na, K), 33% free amino acids and related compounds, 20% urea in B. viridis; 43% inorganic ions, 40% free amino acids and related compounds, 17% urea in B. boreas. Free carbohydrates appear to be virtually absent. Increases in intracellular free amino acids and related compounds involve different substances in the 2 species. B. viridis accumulates primarily taurlne, glycine and alanine. B. boreas accumulates primarily taurine, glutamic acid and carnosine. Intracellular urea concentrations seem always to be significantly higher than plasma concentrations.