Studies on Changes in Toughness of the Body Wall from Sea Cucumber

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Holothurian body wall rapidly changes its mechanical properties. However, the mechanisms involved are not fully understood. The present study deals with the cation-dependent changes in toughness of holothurian body wall in association with acidic glycosaminoglycan(AGAG).1. The toughness of the body wall from a sea cucumber Stichopus japonicus was 0.6 to 1.4kg in the absence of salt and decreased markedly by monovalent cations, until it reached zero at 0.3M NaCl or 0.4M KCl. The toughness tended to decrease by CaCl_2 and MgCl_2, though the extent was much smaller.2. The specific viscosity (<eta>sp) of holothurian AGAG decreased from 0.7 in the absence of salt to 0.47, 0.51, 0.49, and 0.57 in 0.1M NaCl, KCl, CaCl2, and MgCl_2, respectively. Increase of salt concentration resulted in a successive decrease of <eta>sp with monovalent cations, whereas <eta>sp rather increased with divalent cations.3. Chemical analyses showed that sea cucumber AGAG contained 19% glucuronic acid, 33% N-acetyl galactosamine and 30% SO^<4->, suggesting that it was a kind of chondroitin sulfate.4. Electron micrographs of the thin sections stained with lead citrate showed many collagen fibrils. By ruthenium red staining of the desalted body wall, AGAG was found to be distributed between collagen fibers and in their peripheral portions. When the body wall was treated with NaCl, there occurred some coagulation of thin fibrils as observed by ruthenium red staining.5. It was suggested from these observations that AGAG plays an important role in toughness changes of the body wall of sea cucumber.