['To measure outer segment phagocytosis in cultures of Royal College of Surgeons (RCS) rat retinal pigment epithelium (RPE) that have been treated with carbachol. Carbachol treatment of RCS RPE results in an increase in the second messenger inositol triphosphate, which mimics that observed in normal RPE after interaction with rod outer segments (ROS).', 'Cultures of RCS RPE were phagocytically challenged with isolated rat ROS for 2 hours. Carbachol (1 mM) was added to some cultures to stimulate inositol triphosphate synthesis, and incubation continued for 30 minutes at 37 degrees C. Inositol triphosphate concentration was measured by radioreceptor assay. Bound and ingested outer segments were quantified by double immunofluorescent staining. Ingestion of outer segment membranes was confirmed by electron microscopy and immunogold staining.', 'Carbachol treatment was associated with a rapid and temporary increase in inositol triphosphate levels. Royal College of Surgeons rat RPE phagocytically challenged with outer segments and treated with carbachol showed significantly higher ingestion (34%) compared to untreated RCS RPE (9%) (P < 0.05).'] Does iP3 generation increase rod outer segment phagocytosis by cultured Royal College of Surgeons retinal pigment epithelium?