Cytochrome c release induced by staurosporine and valinomycin in human medulloblastoma D283 cells. Cultures were incubated for the indicated periods of time with staurosporine (STS) (a), valinomycin (Val) (b), or the vehicle. Cells were fractionated into a cytosolic and a mitochondria-containing nuclear–heavy membrane fraction (Pellet). Immunoblot analysis was performed using an anti-cytochrome c antibody. Blots were incubated with an anti-VDAC antibody to exclude contaminations of the cytosolic fraction with mitochondria. An anti-α-tubulin antibody was used as loading control. The experiment was repeated three times with similar results. c, Immunoblot analysis of whole-cell lysates using an anti-cytochrome c and an anti-α-tubulin antibody after exposure to STS, Val, or vehicle for the indicated periods of time. The experiment was repeated twice with similar results.