9404557 Trotter Echinoderms possess the apparently unique capacity to modulate the mechanical properties of their collagenous tissues by means of neurally regulated secretions. Their collagenous tissues, like those of other animals, are composed of collagen fibrils and a non-fibrillar matrix. The collagen fibrils are short and symmetrically spindle- shaped. They are extensively cross-linked and are chemically and physically stable over long periods of time. The physiological changes in tissue mechanics are not produced by changes in the molecular structure of the collagen fibrils by changes in the capacity of the interfibrillar matrix to transfer stress between the short fibrils. A principal component of the echinoderm interfibrillar matrix is proteoglycan (PG), including fibril surface-associated PG. The mechanical modulations that are produced in echinoderm collagenous tissues by changing the ionic environment have suggested that the electrochemical properties of glycosaminoglycans (GAGs) are important determinants of the tensile properties of the tissues. However, no experiments have yet been done to directly test this hypothesis. The experiments proposed here are designed to test it using biochemical and biophysical analyses on isolated components. Native collagen fibrils with their surface associated PGs will be isolated from the deep dermis of sea cucumbers and the spine ligaments of sea urchins. Their interactions will be studied using light scattering and viscometric analyses. The PGs and their GAG moieties will also be isolated and purified, and the interactions of these molecules will be analyzed. The associations of fibrils and molecules will be studied as a function of the specific ion composition of the medium in order to define their electrochemical properties. The hypothesis that organic molecules is secreted by effector cells modulate matrix interactions by modifying GAG-GAG interactions will be tested by identifying "plasticizer" an d "stiffener" molecules. Their ability to modify the interactions of fibrils, PGs and GAGs, will be determined. These studies should yield significant new information on the role of echinoderm PGs and GAGs in transferring stress between collagen fibrils and thereby determining tissue mechanical properties. They should further lead to the identification of the physiological modulators of tissue mechanics, and to a definition of their modes of action. ***
