Mineral Content and Salt-dependent Viscosity in the Dermis of the Sea Cucumber Cucumaria frondosa

Abstract

Samples from the deep dermis of the sea cucumber Cucumaria frondosa were analyzed to determine the concentrations of Na, K, Ca, and Mg in fresh tissues as well as in those that had been incubated in filtered seawater or extracted extensively in deionized water. Fresh tissues were in equilibrium with seawater with respect to the above minerals, and showed a relative concentration of K, Mg, and Ca. Water-extracted tissues were enriched in Mg and Ca and depleted in K and Na. The Ca and Mg could be removed from the tissues by extraction in a divalent cation chelator or in 0.1 M HCl. Biomechanical (creep) tests showed that dermal specimens in which the resident cells had been lysed by freezing and thawing had very low viscosities in buffered solutions of a divalent cation chelator containing either 0.03 M or 1.0 M NaCl. In contrast, their viscosities were quite high in similar solutions containing 0.3 M NaCl. The aggregation of isolated collagen fibrils in the presence of the dermal glycoprotein stiparin showed a similar dependence on the concentration of NaCl: the fibrils aggregated in 0.3 M NaCl, but not in 0.03 or 1.0 M NaCl. The above results are inconsistent with the hypothesis that collagen fibril interactions in C. frondosa dermis are regulated by cellular control of the extracellular [Ca 2+]. The results are consistent with the hypothesis that stiparin mediates mechanical interactions between collagen fibrils in dermal tissues as well as in isolated fibrils.