CALCIUM UPTAKE AND EXCHANGE IN LEG NERVES OF THE CRAB ‘LIBINIA EMARGINATA’

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Abstract
—: The kinetics of washout of radioactive calcium (45Ca) from nerves of the larger legs of Libinia emarginata equilibrated in various solutions of artificial sea water (ASW) containing 1, 11, 22 or 44 mM‐Ca was followed. In every case two components were found when the period of washout was not more than 30 min. The washout of 14C labelled inulin and sucrose gave one and two components respectively; these substances were considered to exist in the extracellular regions of nerve fibers. Comparison of the total calcium of the nerves determined spectrophotometrically and by measurement of radioactivity indicated that the exchangeability of calcium in the nerves in ASW containing 44 and 22 mM‐Ca was 100%. In the case of nerves equilibrated in 11 mM‐CaASW, two groups of nerves, one (group A) containing a high concentration of Ca (13.6 μmol/g) and the other (group B) containing a low concentration (7.3 μmol/g), were detected Several factors which could account for the accumulation of Ca in nerve fibers in group A were considered. The electrolyte data relating to group A nerve fibers indicated that Ca accumulation may be due to the presence of a high concentration of sodium in those fibers. However, the exchangeability of Ca for group A was about 47%; and in group B fibers, it was 61%. The exchangeability was less than 41% in the case of nerves equilibrated in 1 mM‐CaASW. The kinetic parameters of 45Ca washout from the nerve fibers have been used to develop a model for the distribution of calcium among the different compartments of the nerve fibers.

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