In A–D, SK-N-SH cells were treated with 0.5 mM paraquat, 2.5 mM MPP+ or 4 µM rotenone for the time indicated. Then, cells were stained with Mitosox (mitochondrial O2•−) or propidium iodide (cell death), and analyzed by FACS. Histogram in A depicts the changes in the Mitosox mean fluorescence in response to paraquat. In B–D, data are expressed as O2•− production (Mitosox fluorescence) and cell survival (% of cells with low Propipdium iodide staining) normalized against control values. Experiments and plots in A–D are representative of at least three independent experiments. In E, cells were treated with 0.5 mM paraquat, 2.5 mM MPP+ or 4 µM rotenone for 48 h. Then, cells were co-stained with DHE (cytosolic ROS) or MitoSOX (mitochondrial ROS) and analyzed by FACS. Results are represented as the increase in DHE or MitoSOX mean fluorescence with respect to controls and are means ± SE of three replicas.