Table 3. Values of model parameters that... | Rockefeller University Press

Table 3.

Values of model parameters that best simulated photocurrents in dark-adapted bass single cones: Response to 10-msec light flashes

	Parameters	Category^a	Units	Cone 1		Cone 2		Cone 3		Mean ± SD^b
VP*	Intensity	Statistical	VP*	167	17,443	174	17,136	173	7,720	Fig. 4
	$γ_{m a x}$	Adjustable	µM/s	100^c	65	100	70	105	68
	$μ_{0}$	Invariant	1/s	0.5	0.5	0.5	0.5	0.5	0.5	—
	$ω_{λ}$	Invariant		0.1	0.1	0.1	0.1	0.1	0.1	—
T*	$Ψ_{0}$	Adjustable		230^d	230^d	215	215	230	230	231 ± 19
	$ω_{a c t}$	Invariant		0.69^e	0.69^e	0.69^e	0.69^e	0.69^e	0.69^e	—
PDE*	$β_{s u b}$	Adjustable	µM/s per molecule	0.185	0.185	0.323	0.323	0.416	0.416	0.334 ± 0.091^f
	$α_{PDE}$	Adjustable	1/s	17^g	47	7	19	14	28	Fig. 4
CNG ion channel	$I dark$	Statistical	pA	22.2	22.2	18.8	18.8	42.3	42.3	27.3 ± 10.5
Ca²⁺ buffer	$K_{H A}$	Adjustable	µM	0.030	0.030	0.044	0.044	0.091	0.091	0.052 ± 0.025
	$C_{H A}$	Adjustable	µM	21.4	21.4	4.6	4.6	66	66	20.9 ± 12.9
	B	Adjustable		10.6	10.6	7	7	15	15	11.5 ± 3.9
Ca²⁺ efflux	$J_{C a}^{\max}$	Statistical	pA	4	4	3.23	3.23	7.63	7.63	4.87 ±1.88^h
	$K_{C a}^{e x c}$	Adjustable	µM	0.025	0.025	0.005	0.005	0.025	0.025	0.019 ± 0.009^h

	Parameters	Category^a	Units	Cone 1		Cone 2		Cone 3		Mean ± SD^b
VP*	Intensity	Statistical	VP*	167	17,443	174	17,136	173	7,720	Fig. 4
	$γ_{m a x}$	Adjustable	µM/s	100^c	65	100	70	105	68
	$μ_{0}$	Invariant	1/s	0.5	0.5	0.5	0.5	0.5	0.5	—
	$ω_{λ}$	Invariant		0.1	0.1	0.1	0.1	0.1	0.1	—
T*	$Ψ_{0}$	Adjustable		230^d	230^d	215	215	230	230	231 ± 19
	$ω_{a c t}$	Invariant		0.69^e	0.69^e	0.69^e	0.69^e	0.69^e	0.69^e	—
PDE*	$β_{s u b}$	Adjustable	µM/s per molecule	0.185	0.185	0.323	0.323	0.416	0.416	0.334 ± 0.091^f
	$α_{PDE}$	Adjustable	1/s	17^g	47	7	19	14	28	Fig. 4
CNG ion channel	$I dark$	Statistical	pA	22.2	22.2	18.8	18.8	42.3	42.3	27.3 ± 10.5
Ca²⁺ buffer	$K_{H A}$	Adjustable	µM	0.030	0.030	0.044	0.044	0.091	0.091	0.052 ± 0.025
	$C_{H A}$	Adjustable	µM	21.4	21.4	4.6	4.6	66	66	20.9 ± 12.9
	B	Adjustable		10.6	10.6	7	7	15	15	11.5 ± 3.9
Ca²⁺ efflux	$J_{C a}^{\max}$	Statistical	pA	4	4	3.23	3.23	7.63	7.63	4.87 ±1.88^h
	$K_{C a}^{e x c}$	Adjustable	µM	0.025	0.025	0.005	0.005	0.025	0.025	0.019 ± 0.009^h

Values of invariant parameters first used to compute dark current are not repeated here. They have the same values listed in Table 2.

Mean ± SD; n = 18 single cones.

$γ_{m a x}$ experimental value is 100–150 s⁻¹ (Tachibanaki et al., 2005).

This value was initially constrained to 150 s⁻¹ from experimental data (Leskov et al., 2000).

Experimental data (Gibson et al., 2000).

Experimental values of PDE* $k_{c a t}$ range from 2.2 to 8 × 10³ s⁻¹ (Dumke et al., 1994; D’Amours and Cote, 1999; Muradov et al., 2009). From the definition of $β_{s u b}$ (Eq. 3.11) and the highest $k_{c a t}$ value, the 0.334 value indicates the effective intracellular volume for cGMP is, on average, 0.08 pL, rather than the 0.19 pL used throughout these calculations. This factor of approximately two can probably be accounted for by the fact that the volume, in fact, changes some from cell to cell and is not the rigid assigned value of 0.19 pL. There is experimental uncertainty because the size of each and every cone recorded from was not measured. Also, the actual concentration of cGMP may be a little smaller than the computed value because there is intracellular cGMP binding (Olson and Pugh, 1993), a fact that would be revealed as a smaller apparent volume.

This value was initially constrained to 10 s⁻¹ at dim lights from the analysis of dark current noise in bass single cones (Holcman and Korenbrot, 2005).

With these values, the computed time constant of Ca²⁺ clearance from bass cone outer segment is 40.0 ± 15.4 msec, similar to the experimental value of 43 ± 9.8 msec in the tiger salamander cone (Sampath et al, 1999).

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