Table 1. Variables and parameters in the model.
Symbols | Implications | Values |
L, L1, L2 | ligand concentration | Variable (in nM) |
R, R1, R2 | number of free surface receptors | Variable |
Ri, R1i, R2i | number of intracellular free receptors | Variable |
LR*, L1R1*, L2R2* | number of active receptor-ligand complex | Variable |
LRd, L1R1d, L2R2d | number of desensitized receptor-ligand complex | Variable |
LRi, L1R1i, L2R2i | number of internalized receptor-ligand complex | Variable |
Rtot | total number of receptors | 25,000 [25] |
kf | ligand receptor association rate | 8.4×107 M−1 s−1 [23], [35] |
kr | low-affinity ligand receptor dissociation rate | 0.37 s−1 [23], [27] |
kdes | desensitization rate | 0.065 s−1 for desensitizable receptor[23], [27]; 0 for nondesensitizable receptor |
ki | internalization rate | 0.0033 s−1 [23], [36] |
kup | up-regulation rate | 0.004 s−1 [23], [24] |
Lmax, L1max, L2max | highest concentration at the gradient center | 17.6 nM [25] if no additional caption |
L0 | basal ligand concentration | 0 nM [25] |
A | radius of the gradient region | 1000 µm [25] |
ρ, ρ1, ρ2 | distance from the gradient center | Variable (in µm) [25] |
n | power of the gradient function | 3 [25] |
The numerical values for parameters are the same for both ligand-receptor pairs unless stated otherwise.