Molecular Vision: Lamb, Mol Vis 2016; 22:674-696. Table 2

Table 2. Downstream phototransduction cascade parameters.

Symbol	Description	Default value ^a	Model 1 value ^b	Units
β_Dark	Dark rate constant of cGMP hydrolysis	3.2	4	s⁻¹
α_max	Maximal rate of cGMP synthesis by GC	120	150	µM/s
f_Ca	Fraction of CNGC current carried by Ca²⁺	0.12
K_GCAP	Ca²⁺ concentration parameter of GCAP	80		nM
m_GCAP	Ca²⁺ cooperativity of GCAP	1.5
J_cG, max	Maximal CNGC current for the OS	2000		pA
K_cG	cG concentration parameter of CNGC	20		µM
J_ex, max	Maximal exchange current for the OS	4.6		pA
K_ex	Ca²⁺ concentration parameter of exchanger	1100		nM

	Calculated resting dark state
cG_Dark	Dark cGMP concentration	4.12	µM
Ca_Dark	Dark Ca²⁺ concentration	322	nM
J_Dark	Dark current	18.4	pA

	Other kinetic parameters
ν_RE	Rate of G-E activation by an R*	300 ^c		s⁻¹
k_E	Rate of G-E shut-off	5 ^c		s⁻¹
β_sub	Rate constant of cGMP hydrolysis by an E*	0.024 ^d	0.063 ^d	s⁻¹
B_Ca	Buffering power of cytoplasm for Ca²⁺	50
V_cyto	Available cytoplasmic volume of OS	0.02		pL

	Longitudinal diffusion parameters
D_cG	Longitudinal diffusion coefficient for cG	40	µm²/s
D_Ca	Longitudinal diffusion coefficient for Ca²⁺	2	µm²/s
L	Length of outer segment	22	µm

a. All values apply to the entire outer segment; however, suction pipette experiments record only a fraction of the total current. b. The default values applied in all cases, except for the three values listed under Model 1. c. The formation (ν_RE) and shut-off (k_E) of E* are modeled as either deterministic or stochastic. d. For comparison with the values used in Gross et al. [11], note that they employed a different parameter for hydrolysis by E*, that they referred to as β_idv, which is shown in Appendix 1 to be related to β_sub by β_idv = N_disks β_sub, where N_disks = 710 is the number of disks in the outer segment.