Decalcification for electron microscopy with L-ascorbic acid

Chemistry, histochemistry and microscopy of the organic matrix of spicules from a gorgonian coral. Relationship to alcian blue staining and calcium binding

Alcian blue dye normally binds to polyanionic, polymeric substances. Such structures are often associated with calcium binding portions of the organic matrix in calcifying tissues. The organic matrix of spicules prepared from the gorgonian Pseudoplexaura flagellosa (Houttuyn) is alcianophilic. The dye is very tightly bound to the lipoid portion of the insoluble spicule matrix. No acidic substances (sulfated or acidic polysaccharides or phospholipids) were demonstrable in this material, suggesting an unusual but unknown interaction between dye and substrate. On a microscopical basis, inclusion of Alcian blue (or Ruthenium red) is an essential co-requisite to glutaraldehyde fixation. Without the dye the morphological integrity of the spicule is lost on decalcification. The fragmented matrix is still alcianophilic suggesting that the dye may substitute for material solubilized by the decalcifying agents. Examination of post-decalcification supernatants demonstrate that approximately 13% of the matrix is solubilized on demineralization, releasing 93% of the carbohydrate but less than 20% of the protein. Liberated protein takes the form of peptides ranging from 1100-1500 daltons. The composition of these peptides is a function of the demineralizing agent. Acidic demineralizers produce peptides proportionately high in acidic amino acids, that do not bind calcium. Peptides produced by chelator decalcification appear to bind calcium but other evidence strongly suggests that the binding is due to adsorbed chelator rather than by soluble matrix.