TABLE II.
Kinetics of PDE Activation and Inactivation in Retinal Photoreceptors
| βdark | N d * | N 0 | N d */N 0 | ka | τ21 | τ | |
|---|---|---|---|---|---|---|---|
| s−1 | s−1 | s−1 | ms | ||||
| Bass cone | 0.24 | 60 | 3 × 106 | 1/5 × 104 | 3.7 × 10−4 | 18.5 | 54 |
| Rod | 1–2a , b | 487 | 2 × 107 | 1/4 × 104 | 2.7 × 104b | 1.8b | 555 |
N d *, number of active PDE molecules in dark; N 0, total number of PDE molecules in the outer segment (1/70 PDE/VP, Zhang et al., 2003); ka, PDE forward activation rate; τ21, PDE backward activation rate; τ = 1/(k a + τ21), active PDE lifetime.
a
Hodgkin and Nunn, 1988, and Nikonov et al., 2000, in tiger salamander retina.
b
Rieke and Baylor, 1996, in toad retina.