Table II.
Kinetics of PDE Activation and Inactivation in Retinal Photoreceptors
| βdark |
|
N 0 |
 /N
0
|
ka | τ−1 | τ | |
|---|---|---|---|---|---|---|---|
| s−1 | s−1 | s−1 | s | ||||
| Bass cone | 0.24 | 60 | 3 × 106 | 1/5 × 104 | 0.17 × 10−4 | 0.84 | 1.19 |
| Rod | 1–2a b | 487 | 2 × 107 | 1/4 × 104 | 0.27 × 10−4 b | 1.8 b | 0.55 |
, number of active PDE molecules in the 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; τ−1, PDE backward activation rate 
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.