Effects of Certain Physico-Chemical Agents On the Mechanical Properties of the Catch Apparatus of the Sea-Urchin Spine

The catch apparatus (CA), a collagenous connective tissue which connects the sea-urchin spine to the test, is known to undergo a remarkable change in its mechanical properties. Effects of various physico-chemical factors on the mechanical properties of the CA have been investigated in order to characterize the linkages which are responsible for determining the mechanical properties of the CA. The stress-strain relations obtained by stretching the specimen at a slow constant speed, 7 μm s−1, were taken as a measure of the viscous resistance of the CA. The viscous resistance of the CA depended largely on the pH and the ionic strength of the medium. It increased with increasing pH and with decreasing ionic strength. The viscous resistance was markedly reduced in a Ca-free medium containing 5 mM-EGTA. It is suggested that linkages sensitive to low pH and those mediated by Ca2+ play a significant role in determining the mechanical properties of the CA.