Mechanisms of intracellular isosmotic regulation: Extracellular space of the shore crabCarcinus maenas in relation to environmental salinity

Abstract

1. In shore crabsCarcinus maenas, which had been maintained for one month in 10, 20, 30, 40, and 50‰ salinity, the extracellular space was estimated by means of the dilution of the food dye amaranth and the polyglycan14C-inulin. 2. The extracellular space does not differ significantly in response to the external salinity. It varies between 29.2 and 36.0% (with a mean of 33.1%) of body weight when estimated by dilution of amaranth and between 16.7 and 18.5% (with a mean of 17.9%) of body weight when estimated by14C-inulin dilution. Differences of values in regard to the substances used for estimation are discussed. 3. The results confirm that the magnitude of the extracellular space is not involved in phenomena of osmoregulation. 4. The rapid reduction in the concentration of haemolymph proteins after transfer of freshwater and marine decapods from lower to higher salinities (Drilhon-Courtois 1934,Siebers et al. 1972) implies, on the basis of the present results, also a reduction in the total amount of haemolymph protein in the crab, since the protein-distribution volume remains unchanged within a wide variety of salinities. The assumption that haemolymph proteins participate in the increase of intracellular free amino acids during isosmotic intracellular regulation is confirmed.