The distribution of actin in cultured normal and dystrophic rat pigment epithelial cells during the phagocytosis of rod outer segments.

In the previous article the authors reported that the ingestion phase of phagocytosis is defective in cultured dystrophic rat pigment epithelial (PE) cells. When these cells are challenged with isolated rod outer segments (ROS), attachment of ROS to the PE cell surfaces occurs to a normal extent. However, only a small number of these bound ROS are subsequently ingested. This raised the possibility that the contractile protein actin might not function normally in the dystrophic rat PE cells, since actin is intimately involved in the ingestion mechanism in other phagocytic cells. Utilizing actin antibodies and the technique of indirect immunofluorescence, we have studied the distribution of actin in cultured normal and dystrophic rat PE cells. Results show that the arrangement of actin fibers in the dystrophic cells appears normal both before and during the attachment of ROS to the cell surfaces. With the additional use of an ROS antiserum to label externally bound ROS, it is also possible to show that actin is involved with the ingestion of ROS by both normal and dystrophic PE cells. Thus, it appears that actin can function normally in dystrophic PE cells, but that the ingestion mechanism becomes activated at only a few sites of ROS attachment. The results of a scanning electron microscope study support this conclusion and also show the presence of a saucer-shaped elaboration of the PE cell plasma membrane beneath attached ROS. These may correspond to the actin feltworks seen with immunofluorescence microscopy at sites of ROS attachment.