Impulse response of the EGFR and GPCR systems. (A&C) The dimensionless response to a ligand impulse was computed for EGFR (A) and GPCR (C). The response is to a ligand impulse of magnitude 0.01K
nM. System responses were computed either by numerically integrating the ODEs governing the system (solid lines) or by inverting the transfer function, G(s) of the linearized system of equations (dotted lines). (B&D) The relaxation time is plotted as function of the extent of downregulation, D (= k
) for the EGFR (B) and the desensitization rate, k
for the GPCR (D). Note that the relaxation time in panel D is plotted on a logarithmic scale to capture the large change in GPCR relaxation time magnitude. This plot would be qualitatively similar to panel B when a linear scale is used.