Symbol | Value/Unit | Interpretation/comment | ||
---|---|---|---|---|

V_{cyto} | 1.0 pl | Volume of the outer segment cytoplasm | ||

J_{dark}/f_{se} | 70 pA | Dark/circulating current measured by suction electrode (s.e.) divided by s.e. collecting efficiency *‡§ | ||

f_{Ca} | 0.1 | Fraction of inward circulating current carried by Ca^{2+‡} | ||

Ca_{dark} | 385 nM | Dark/resting concentration of Ca^{2+}_{i} in outer segment; see ii‡ | ||

J_{ex,sat} | 12.5 pA | Saturated magnitude of Na^{+}/Ca^{2+}-K^{+} exchange current‡ | ||

K_{ex} | 1600 nM | Ca^{2+}_{i} giving rise to half-maximal exchange current‡ | ||

K_{Ca} | 100 nM | Ca^{2+}_{i} at which cyclase activity is half-maximal§ | ||

n_{Ca} | 2.0 | Cooperativity coefficient for Ca^{2+} dependence of cyclase activity§‖ | ||

β_{dark} | 0.8–1.2 s^{−1} | Rate constant of cGMP hydrolysis in dark‖¶ | ||

α′_{max} | 10–15 s^{−1} | Maximum rate of cGMP synthesis divided by cG_{dark}¶ | ||

γ | 5.6 s^{−1} | Factor for converting Ca^{2+} currents into concentration changes; Eq. 15 | ||

η | 0.8 | Fraction of unused exchange current capacity at rest; Eq. 15 | ||

μ | 2.7 s^{−1} | Real component of the oscillatory term governing cyclase feedback near Ca_{dark}; Eqs. 15, 20, and A6.8 | ||

ν | 4.5 s^{−1} | Imaginary component of the oscillatory feedback term; Eqs. 20 and A6.8 | ||

θ | 3.8 radians | Phase term of the calcium feedback; Eqs. 20 and A6.8 |

Parameters in rows 1–8 were fixed at the values listed, based on the references. β

_{dark}was varied within the range given to optimize fitting; the most commonly used value was 1.0 s^{−1}; in the perturbation analysis α′_{max}is not free, but takes a value consequent to initial conditions based on equations 6, 11, and 13 (see Appendix II). The last five parameters in the table arise in the perturbation analysis of the dim-flash response in Ringer's (Theorem 6); the values listed are typical ones.↵* Lyubarsky et al., 1996;

↵‡ Lagnado et al., 1992;

↵§ Koutalos et al., 1995;

↵‖ Pugh et al., 1997;

↵¶ Hodgkin and Nunn, 1988.