The relationship between plasma proteins and intracellular free amino acids during osmotic regulation in Carcinus maenas

Abstract

AbstractThe osmoregulatory behavior of the Adriatic population of the shore crab Carcinus maenas is similar to that of more northern populations. Hyperosmotic regulation of the hemolymph is initiated below about 95–85% seawater (973–871 m Osm/kg) and slight hypo‐osmotic regulation appears to occur above approximately 110% seawater (1,127 m Osm/kg). Extracellular volume is actively regulated, and changes in levels of amino acids imply effective regulation of intracellular volume. Serum protein levels increase immediately after transfer of the crabs from high to low salinity, although the changes are much smaller than those reported by other investigators. Levels of free amino acids in serum decrease after transfer from high to low salinity and labeled leucine is incorporated into hemocyanin at a greater rate after such a transfer than in the absence of a change in salinity. However, the rate of incorporation of leucine is also greater at low than at high ionic strength in vitro, in cell‐free preparations. This result suggests that the experiment does not demonstrate storage of intracellular free amino acids by the extracellular oxygen carrier, but rather reflects “passive” binding to hydrophobic sites on the hemocyanin molecule.