Objective: To investigate the role of cyclic adenosine monophosphate (cAMP) and protein kinase C (PKC) in the phagocytic process of human retinal pigment epithelial (HRPE) cells by measuring phagocytosis indexes in specific and nonspecific phagocytic process.
Method: The cultured HRPE cells were incubated with 1 x 10(7)/ml rod outer segments (ROS) or latex beads (LB) at 37 degrees C, then the phagocytosis were terminated at different incubation time (5 min-48 h). The kinetics of phagocytosis was measured by double-fluorescent vital assay. The binding and ingestion of ROS or LB were proved by scanning and transmission electron microscope. cAMP level was measured using (125)I-cAMP radio-immunity kit, and PKC activity was measured by counting gamma-(32)P radio-activity with liquid scintillation.
Result: In specific phagocytosis of HRPE cells, the binding of ROS was happened at 15 min of incubation, and the cAMP level was decreased at the same time; the activity of PKC (both in cytoplasm and membrane)was decreased at 5 min which was earlier than the changes of the level of cAMP, but both indexes were reached their lowest level at 24 h. In nonspecific phagocytosis of HRPE cells, the binding of LB was happened at 1.5 h; on the other hand, when HRPE cells were incubated with LB, cAMP level did not change until 12 h (P > 0.05), but it began to decrease in the incubation time from 12 h-48 h; the activity of PKC (both in cytoplasm and on membrane) was stable during all incubation periods (P > 0.05).
Conclusion: cAMP and PKC are very important for sustaining the ingestion process in specific phagocytosis of HRPE cells, but have no direct relationship with nonspecific phagocytosis. Furthermore, cAMP level and PKC activity in HRPE cells are decreased during specific phagocytosis.