Effects of FCS depletion on NB4 and NB4-As^Rapoptosis. NB4 (left graph) and NB4-As^R cells (right graph) were grown in the absence (□) or in the presence (▴) of 10⁻⁷ mol/L As₂O₃ for 3 days. Medium was supplied with the concentrations of FCS indicated in the plot. Apoptosis (%) was determined, after a TUNEL assay, by flow cytometry. Each value represents the mean ± SD of three independent measurements.