A histochemical study of calcium storage in the foot of the freshwater gastropod, Helisoma duryi eudiscus (Pilsbry)
Shortly after hatching, calcium appears in the form of numerous spherules within the connective tissue of the foot of Helisoma. Concomitantly, there is a change in the histochemical demonstration of sulfated mucopolysaccharides, glycogen, and alkaline phosphatase. The sulfated mucopolysaccharide component of the mucous glands and the mucous coating of the foot increase in staining intensity. Similarly, the glycogen content of the foot epithelium and subepithelial connective tissues increases in staining intensity. Also, alkaline phosphatase first appears and exhibits an intense staining reaction within the foot epithelium. It is suggested that the coincidental appearance of these substances is related to the percutaneous absorption and storage of calcium. It is proposed that the sulfated mucopolysaccharides absorb calcium from the environment, that this calcium–mucous complex is hydrolyzed by the alkaline phosphatase, that the released calcium becomes bound to the fibers and sulfated mucopolysaccharides forming the matrix of the spherules, and that the calcium is accumulated in the form of such spherules.