Diurnal changes of lysosomes including ultrastructural changes of phagosomes and acid phosphatase reactions in phagosomes, as well as diurnal biochemical changes in cathepsin D activity, were studied in the retinal pigment epithelium (RPE) of the rabbit. The rabbit was maintained on a natural light-dark cycle over seven days in fall and was sacrificed at various times during the day and night. The number of lysosomes or phagosomes in the RPE was the highest at 1.5 hours after exposure to sunlight (8:00 AM), and thereafter decreased with time. Three types of phagosomes were observed and acid phosphatase reactions were different in each type of phagosome; the fresh phagosomes were negative or positive, lamellar bodies positive, and dense bodies partially positive. The biochemical activity of cathepsin D was the highest at 8:00 AM, and this was consistent with the time of peak in phagocytic activity in the RPE. This report shows that phagocytic activity in the RPE occurred in the early stage after exposure to sunlight, and that fresh phagosomes were sequentially degraded to lamellar or dense bodies. Cathepsin D activity also increased, and this was consistent with the phagocytic activity in the RPE.
Acid Phosphatase/metabolism ; Animals ; Cathepsin D/metabolism ; Cell Count ; Choroid/metabolism/ultrastructure ; Circadian Rhythm/*physiology ; Lysosomes/*metabolism/ultrastructure ; Phagosomes/*metabolism/ultrastructure ; Pigment Epithelium of Eye/*metabolism/ultrastructure ; Rabbits

This study explored the role of radiation-induced autophagy in low-dose hyperradiosensitivity (HRS) in the human lung cancer cell line A549. A549 cells, either treated with an autophagic inhibitor 3-methyladenine (3-MA), or with a vehicle control, were irradiated at different low doses (≤0.5 Gy). The generation of autophagy was examined by laser scanning confocal microscopy. Western blotting was used to detect the expression of microtubule-associated protein l light chain 3B II (LC3B-II). Flow cytometry (FCM) and clonogenic assays were used to measure the fraction of surviving cells at the low irradiation doses. Our results showed that there was a greater inhibition of autophagic activity, but a higher degree of low-dose HRS in A549 cells treated with 3-MA than in control group. Our data demonstrated that radiation-induced autophagy is correlated with HRS in A549 cells, and is probably one of the mechanisms underlying HRS.
Adenine ; analogs & derivatives ; pharmacology ; Autophagy ; drug effects ; radiation effects ; Blotting, Western ; Cell Line, Tumor ; Cell Survival ; drug effects ; radiation effects ; Dose-Response Relationship, Radiation ; Flow Cytometry ; Green Fluorescent Proteins ; genetics ; metabolism ; Humans ; Lung Neoplasms ; genetics ; metabolism ; pathology ; Microscopy, Confocal ; Microscopy, Electron, Transmission ; Microtubule-Associated Proteins ; genetics ; metabolism ; Phagosomes ; drug effects ; radiation effects ; ultrastructure ; Radiation Tolerance ; drug effects ; radiation effects