Time evolution of the threshold distribution and adaptation. The ATP threshold distribution for the cell type "Bcl-xL 1E1" is shown at different time points after IL-3 growth removal together with the dynamics of the intracellular ATP level (red thick line). The distribution is normalized to the survival fraction S (a(t)). The values of the parameters of the model are the same as in Figure 2. In this case, adaptation observed in the late stages of the response is the result of the combined effects of high threshold variability with intracellular ATP adapting to a new steady state.