Response of CEM cells to electroporated cytochrome c. (Upper panel) CEM cells were coelectroporated with 80 μg/mL cytochrome c and 8 μg/mL cytochrome c-biotin-streptavidin-FITC as described in the text, using different electroporation conditions. Gates were set using Coulter fluorospheres. Cells were analyzed 1 hour after electroporation. (A) Control cells (exposed to labeled cytochrome c without electroporation); (B) 240 V, 960 μF; (C) 240 V, 500 μF; (D) 240 V, 250 μF. In (B), 43% of gated cells were FITC-positive. Note that successful electroporation was achieved only with 240 V and 960 μF. (Lower panel) DNA analysis of cultures A through D 2 hours after electroporation. Similar DNA profiles were obtained after 4, 6, and 24 hours. Note the absence of apoptosis induction by cytochrome c.