Kinetic parameters for the different processes displayed in Figure 1.

-Units are given in the SI system although most results were expressed in conventional units, for instance, nM instead of .-The rate constants and to are related to processes that take place through the interface that separates the cell surface and the inside the cell and do not correspond with the rate constants used in refs. [21] and [5]. Their values were assigned so that under conditions where spatial gradients of concentration become less significant the solutions computed behave like those obtained by using non-spatial models. For the rest of the trafficking parameters the average values for the EGF signaling pathway reported in ref.[21] were used.-Initial conditions: , . In simulations with a single input dose of ligand was added to the extracellular medium.