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. 2022 Feb 16;42(7):1254–1274. doi: 10.1523/JNEUROSCI.0793-21.2021

Table 2.

Parameters and best fit values for cone phototransduction biophysical model with fast adaptation only

Parameter Symbol Units Type Fit values
Fig. 9 Figure 9 D–F Figure 9 G–H Figure 12 Figure 13
Opsin gain Γ unitless Free 3.0 8.92 10.0 1.4 18.0
Opsin decay rate constant σ s-1 Locked 23.5 23.5 23.5 23.5 23.5
PDE decay rate constant ϕ s-1 Constrained (ϕ = σ) 23.5 23.5 23.5 23.5 23.5
PDE dark activation rate η s-1 Locked 2395 2395 2395 2395 2395
cGMP-to-current constant k pA2µM-3 Fixed 0.02 0.02 0.02 0.02 0.02
cGMP channel cooperativity h unitless Fixed 3 3 3 3 3
Ca2+ extrusion rate constant β s-1 Locked 9 9 9 9 9
Fraction of current carried by calcium q unitless Derived 0.0662 0.031 0.1125 0.0556 0.078
Maximal cGMP synthesis rate by GC Smax s-1 Derived 27 153 34 950 22 752 28 784 25 677
Ca2+ GC affinity KGC µM Locked 0.5 0.5 0.5 0.5 0.5
Ca2+ GC cooperativity m unitless Fixed 4 4 4 4 4
Ca2+ concentration in darkness Cadark µM Fixed 1 1 1 1 1
cGMP concentration in darkness cGMPdark µM Derived 18.95 24.39 15.87 20.08 17.92
Dark current Idark pA Measured −136 −290 −80 −108 −115