A change in protein concentrations can switch the type of the TGF- β response. (A) Percentage of parameter sets that permit a switch in the qualitative response (transient versus stustained response) to ligand when TGF-β Receptor, R-Smad or Co-Smad concentrations are increased or decreased by 100-fold. The parameter sets were drawn from the ranges as specified in Additional file 2, Table S1 (black), or in more (grey) and more (light grey) restricted ranges as shown in Additional file 3, Fig. S7. (B) The minimal relative change that is required in the concentrations of TGF-β Receptor (black), R-Smad (grey), or Co-Smad (light grey) to switch between transient and sustained responses when parameters were drawn from the most restricted range (corresponding to the light grey column in panel A and the lightest colour in Additional file 3, Fig. S7.