Calcium-containing lysosomes in the outer mantle epithelial cells of Amblema, a fresh-water mollusc.

The cells of the outer mantle epithelium contain numerous large pleomorphic electron dense bodies. In their fine structure they resemble lysosomes. Positive acid phosphatase histochemistry confirms that these supranuclear and subnuclear structures are lysosomes. A major portion of the intralysosomal material is resistant to high-temperature microincineration, indicative of an inorganic component. Subsequent microprobe analyses identified considerable calcium within these organelles. Such entities are similar in structure and ionic content to the lysosomes of avian intestinal absorbing cells, another calcium-transporting epithelium. These mantle lysosomes may function in transcellular calcium transport during shell formation, growth, and repair, especially since the mantle is the shell-forming organ in molluscs.