Kinetic parameters for Ih and HCN isoforms
| HCN isoform | V1/2 ± SD (mV) | t ± SD at −94 mV (ms) |
|---|---|---|
| Rod Ih | −77 ± 0.78 (n = 10) | 52.3 ± 9.5 (n = 4) |
| Cone Ih | −74 ± 1.1 (n = 10) | 50.7 ± 8.0 (n = 8) |
| HCN1 | −69 | 84 |
| HCN2 | −95 | 557 |
| HCN3 | −77 | 1408 |
| HCN4 | −81 | 3586 |
Values for rod and cone Ih are very similar. Kinetic data for both rods and cones are similar to HCN1. Data for HCN1–HCN4 come from measurements from homogeneous expression systems (Altomare et al., 2001; Stieber et al., 2005). The half-activation voltage for HCN1 is known to be ∼5 mV more hyperpolarized in in vivo systems than in the expression system (Altomare et al., 2001).