ABSTRACT
Ultrastructure of catch connective tissue was compared in relaxed state and in catch state. The catch connective tissue is the collagenous connective tissue that changes its mechanical properties rapidly under nervous control. Calcium seems to be involved in the change, because manipulation of calcium ion concentration profoundly affects the mechanical properties. In the present study, samples were treated with a fixative containing 2.5% pyroantimonate to identify possible calcium storage sites. The material used were dermis of the sea cucumber, Stichopus chloronotus. The relaxed sample was cut out from the animal which was anesthetized by cooling. The catch state was induced by application of artificial sea water with elevated potassium concentration (100 mM) to the isolated dermis. In the relaxed state, pyroantimonate precipitates were found in two kinds of cells: one was the vacuole cell which is reported for the first time in this study; the other was the neurosecretory cell with granules. The vacuole cell had processes which were packed with vacuoles of 0.4–0.7 µ m in diameter; the processes were found all over the dermis. Analysis with an energy dispersive X-ray microanalyzer suggested that the precipitates, both in the vacuoles and in the granules, contained calcium. In the catch state, the precipitates were not observed in the vacuoles but they remained in the granules. The present results suggest that calcium ions are stored in the vacuoles and they are released to induce connective tissue catch.
