Dynamic model validation: receptor internalization. Simulation results for receptor internalization at 100 nM insulin (blue) as well as those without insulin (red) are shown and compared to experimental data . Surface receptors were radioactively labeled. This was simulated by setting the initial conditions such that all receptors are in the state R at the plasma membrane. Note that the receptor model is linear for constant insulin concentration. Therefore, the assay can be simulated with this choice of initial conditions.