Abstract
Outer segment fragments discarded by rod photoreceptors are phagocytized by the pigmented retinal epithelium (PE). Within the PE, lysosomes interact with the phagosomes and then lysosomal enzymes degrade the outer segment debris. The ability of the pigmented retinal epithelium to phagocytize polystryrene spheres was exploited as a means of altering the composition of the phagosomes. A suspension of polystyrene spheres was injected between the retina and its epithelium in Rana pipiens tadpoles. At 2, 4, and 8 days after injection, the retinal epithelium was prepared for acid phosphatase cytochemistry. Around some of the phagocytized beads, acid phosphatase reaction product was observed indicating an interaction between the experimental phagosome and lysosomes. Lysosomes were not observed in the PE cells which contained ingested polystyrene spheres. Our findings suggest that the component of the phagosome necessary for lysosomal interaction is the membrane surrounding the phagosome and not the contents of the phagocytic vesicle.