Figure 8. Direct comparison of the effects of photobleached and untreated melanosomes on the sensitivity of individual ARPE-19 cells to H₂O₂-induced toxicity in co-cultures. A: Merged bright-field and fluorescence images illustrating cells in co-cultures containing either untreated granules (identified by co-phagocytosis of marker fluorescent beads detected by 542 excitation/612 emission [shown red, two upper cells]), or containing photobleached granules (identified by marker beads with 468 excitation/508 emission [shown green, lower cell]). Scale bar: 10 μm. B: Live cell imaging of dynamic changes in nuclear PI fluorescence for co-cultured cells pre-loaded with untreated (mel) or photobleached melanosomes (pb mel) and treated with 800 μM H₂O₂. Numbers of cells containing the different particle types pre-selected for analysis were as follows: mel, n=38 (black circles); pb mel, n=32 (open circles). Data are the percent of the pre-selected cells in each particle group surviving (no nuclear PI) with time. The shift to the left of the curve for pb mel illustrates the magnitude of the decreased survival for cells containing pb mel relative to mel. The curves differ significantly (GraphPad Prism 5 survival analysis, p<0.02).