Figure 3. Effect of phagocytosed melanosomes on the sensitivity of ARPE-19 cell populations to H₂O₂-induced toxicity. Dynamic changes in propidium iodide (PI) fluorescence (in arbitrary units [AU]) in ARPE-19 cultures treated with A: 200 μM H₂O₂ or B: 16 mU/ml glucose oxidase (GOx) to generate H₂O₂ enzymatically. Cells were pre-loaded by phagocytosis with latex beads (triangles), untreated melanosomes (mel, black circles) or photobleached melanosomes (pb mel, open circles). Data are the means of 3 replicate culture wells per treatment group within representative experiments of each type. Accompanying tables show the corresponding quantitative data. Onset times, mean slopes and peak intensities are as described in Figure 1B and Table 1. Single asterisks indicate where the outcome for that parameter differs significantly from the latex bead control; double asterisks indicate where pb mel differs significantly from mel (unpaired t tests with equal variances, p<0.02).