Valinomycin does not activate neural apoptosis.a, D283 medulloblastoma cells were treated with vehicle (Con), Val, or STS for up to 24 hr. Caspase-3 like activity was measured by cleavage of the fluorigenic substrate Ac-DEVD-AMC. Activities are presented as increase in AMC fluorescence (in arbitrary fluorescence units) over 60 min per microgram of protein. Data are means ± SEM from n = 8 cultures, and experiments were repeated three times with similar results. Different from controls, *p < 0.05. b, Immunoblot probed with an antibody recognizing procaspase-3 and active caspase-3. Cultures were exposed to vehicle (Con), Val, and STS for 6 hr. Experiment was repeated twice with similar results.c–e, Hoechst staining of D283 cells treated with vehicle (c) or Val (d) for 20 hr. Exposure to Val induced no chromatin condensation in contrast to cells treated with STS for 6 hr (e). Scale bar, 50 μm.