Endocytosis and aspects of autophagy in the foot epithelium of the slug Agriolimax reticulatus (Müller)

Abstract

The foot epithelium of the slug Agriolimax reticulatus (M) can function as a digestive epithelium and possesses a vacuolar system in which heterophagic and autophagic material is hydrolysed. Using ferritin and peroxidase as markers, the process of endocytosis has been demonstrated at the level of the electron microscopy. The mechanisms involved with the uptake of each marker differed in that ferritin was confined to fairly large vacuoles, while peroxidase was present in smaller pinocytotic vesicles which ultimately fused to form larger vacuoles or multivesicular bodies. Cytochemical tests for acid phosphatase revealed that the latter bodies acquired hydrolytic enzyme to become secondary lysosomes. Acid phosphatase was also localized in the Golgi apparatus of the epithelial cells. In addition to the endocytotic activity, evidence of autophagy was found in the epithelial cells and this process was apparently enhanced during starvation.