Abstract
Catch connective tissue is collagenous connective tissue that changes its mechanical properties rapidly. Calcium has been assumed to play a key role in the catch mechanism because calcium concentration profoundly affects the mechanical properties. We have found a calcium-storage cell, the vacuole cell, in the dermis of the sea cucumber Stichopus chloronotus a wellstudied catch connective tissue. The processes of this cell are packed with vacuoles measuring 0.1–1.5 μm in diameter. The ultrastructure was compared in a relaxed state and in a catch (stiff) state induced by high-potassium artificial sea water. When fixed with pyroantimonate, the vacuoles contained precipitates in the relaxed state but not in the catch state. Analysis with an energy-dispersive X-ray microanalyzer suggested that the precipitate contains calcium. The release of calcium ions from the vacuole cell is proposed to induce connective tissue catch.
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