Lysosomes and the modulation of cell morphology in the isthmus region of the outer mantle epithelium in the estuarine clam, Rangia cuneata

Abstract

In bivalves, the isthmus region of the outer mantle epithelium lies adjacent to the hinge ligament. In Rangia cuneata, the columnar cells of the epithelium manifest two distinct morphological states which are a function of the animal's environment. In state 1 the cells are uniformly filled with glycogen and in state 2 they contain large spherical whorls of rough endoplasmic reticulum (RER) and are depleted in glycogen. In both states the cells contain large dense inclusions which are residual bodies based on their morphology and small but definite acid phosphatase activity. Based on the stucture of the RER and the cytoplasmic dispositions of residual bodies and other organelles, it is suggested that (1) the residual bodies are derived from autophagic activity originating at the center of RER whorls and (2) that autophagy is responsible for the destruction of the whorls when the cells pass from state 2 to state 1.