A COMPARISON BETWEEN MELANOTIC AND AMELANOTIC RETINAL-PIGMENT EPITHELIAL-CELLS IN-VITRO CONCERNING THE EFFECTS OF L-DOPA AND OXYGEN ON CELL-CYCLE

Melanin precursors and free radicals, cytotoxic substances, are produc ed during melanin synthesis by tyrosinase. We compared these cytotoxic effects of L-dopa and oxygen on the cell cycle of melanotic retinal p igment epithelial (RPE) cells with amelanotic RPE cells because of the differences of tyrosinase activities between melanotic and amelanotic RPE cells. Flow cytometric DNA analysis of RPE cells exposed to L-dop a (100 muM and 250 muM) were conducted at several oxygen concentration s (20%, 10%, and 5%). The dose-dependent effect of L-dopa to arrest th e cell cycle (the S phase) was more pronounced in melanotic than in am elanotic RPE cells, and oxygen caused arrest in the G1 phase.