Glycerinated catch apparatus of sea urchin spines: the effects of cations on its mechanical properties and ultrastructure

Sea urchin spinal ligaments (the catch apparatus) were extracted with glyce rin, and electron microscopic observations comfirmed that no cell membranes remained intact after glycerination. We studied the effects of cations (Na +, K+, Ca2+, Mg2+) on the mechanical properties of the glycerinated ligamen ts. Monovalent cations decreased whereas divalent cations increased the vis cosity of the ligaments. The ion dependencies were similar to previous resu lts with detergent-extracted holothurian dermis, which suggests that the ec hinoid ligament shares a similar mechanism for changes in mechanical proper ties with other catch connective tissues. This provides evidence against th e hypothesis of del Castillo et al(1995) that muscles in the catch apparatu s are responsible for the changes in mechanical properties of the ligament. Fine projections cross-bridging collagen fibrils were observed in the glyc erin-extracted ligaments as well as in the intact ligaments. They were foun d in all the ionic conditions studied.