Valinomycin reduces staurosporine-induced increase in caspase-3 like protease activity and apoptotic nuclear morphology. a, Apoptotic cell death was induced in D283 cells by an exposure to STS for 6 hr. Val or vehicle was added as indicated. Caspase-3 like protease activity was measured by cleavage of the Ac-DEVD-AMC substrate. Activities are represented as increase in AMC fluorescence over 60 min per microgram of protein. Val significantly reduced STS-induced Ac-DEVD-AMC cleavage. Data are means from n = 8 cultures; experiment was repeated twice with comparable results, *p < 0.05 different from controls.b, Immunoblot analysis of cultures treated with STS, Val, STS + Val or vehicle for 6 hr using an anti-caspase-3 antibody. Addition of Val to cultures treated with STS reduced cleavage of pro-caspase-3 compared with cultures treated with STS alone. Experiment was repeated twice with similar results. c, D283 cells were exposed to STS for 4 hr. Morphology of nuclei was visualized by Hoechst 33258 staining. Percentage of nuclei with fragmented chromatin was determined. n = 4 cultures (700–800 nuclei). Different from controls, *p < 0.05.d, Cell death was induced by exposure to STS for 6 hr. Vehicle or FCCP were added as indicated. Caspase-3 like activity was measured by cleavage of the Ac-DEVD-AMC substrate. Data are means from n = 8 cultures; experiments were done in duplicate and yielded similar results, *p < 0.05 different from controls. e, Determination of cellular ATP content in D283 cells exposed to vehicle, STS, Val, or STS + Val for 3 and 6 hr. Luciferase activity of cultures treated with vehicle was set to 100% activity. Treatment with STS, Val, and STS + Val resulted in a decrease in luciferase activity. Data are means fromn = 4–6 cultures per treatment.