Figure 1. Melatonin protected the retinal pigment epithelium (RPE) cells against H₂O₂ damage, especially in high concentrations (10⁻⁴ M) and luzindole decreased the protective effects of melatonin. Phase-contrast microscopic images of the effects of melatonin and its membrane-receptor antagonist (luzindole) on retinal pigment epithelial cells against H₂O₂ damage. A-F: The RPE cells are from the ARPE-19 cell line (an immortal RPE cell line from a 19-year-old donor). G-L: The RPE cells are from the primary culture (PC) from the donor eye. ARPE-19 and PC cells were cultured with or without H₂O₂, melatonin, and luzindole, as follows: without H₂O₂, melatonin, and luzindole(A and G); with H₂O₂ at 0.5 mM concentrations for 24 h (B and H); with H₂O₂ and a pretreatment of melatonin at 10⁻¹⁰ M (C and I) or at 10⁻⁴ M (D and J) for 24 h; or with luzindole (50 μM, 1 h), followed by melatonin at 10⁻¹⁰ M (E and K) or at 10⁻⁴ M for 24 h (F and L). H₂O₂ was then added and the ARPE-19 and PC cells cultured for 24 h.