ABSTRACT
In this study, the mechanical properties of the collagenous spine ligaments of the sea urchin Eucidaris tribuloides were investigated in vitro. The tensile strength and stiffness of ligaments were relatively high when their artificial sea water (ASW) bathing medium contained from 0.0 to 20mM Ca++. If, however, the Ca++ free ASW bath included EGTA, a calcium chelator, then the strength and stiffness decreased by approximately five-fold. This Ca++ chelation effect was fully reversed by re-addition of Ca++ to 5mM or greater, and partly restored at lower levels of replenished Ca++. Treatment of ligaments with a non-ionic detergent in ASW induced a stiff state that could not be quickly reversed; even after washing in Ca++ free ASW with chelator. This suggests that viable cells are necessary to release the catch state, that they do not release catch by secreting a chelator, and that calcium is not even needed to induce catch. These data support the model proposed by Diab and Gilly (1984) which recognizes the in vitro effects of Ca++ manipulation, but suggests that calcium ions do not directly affect the mechanical state of the extracellular matrix.
