TABLE I.
Rate Data for HCN2 Channels and Fractional Activation Data for CNGA1 Channels
| HCN2 channel | RatecAMP/RateControl | CNGA1 channel | Imax cAMP/Imax cGMP |
|---|---|---|---|
| Wild type (7) | 3.6 ± 0.48 | CNGA1cys-free (14) | 0.055 ± 0.01 |
| K472E (4) | 0.98 ± 0.04 | R431E (5) | 0.95 ± 0.01 |
| E502K (6) | 2.2 ± 0.37 | E462R (5) | 0.38 ± 0.05 |
| K472E + E502K (4) | 2.3 ± 0.52 | R431E + E462R (3) | 0.82 ± 0.04 |
| R431D (5) | 0.92 ± 0.03 | ||
| D542K (5) | 2.7 ± 0.99 | D502R (3) | 0.18 ± 0.03 |
| K472E + D542K (3) | 2.3 ± 1.0 | R431D + D502R (3) | 0.11 ± 0.03 |
| E502K + D542K (5) | 1.0 ± 0.05 |
All values are mean ± SEM. The n values are in parentheses after each channel construct. HCN2 channel rates (1/τ): time constants (τ) were calculated from single-exponential fits to currents in response to voltage pulses to −130 mV, either in the presence or absence of cAMP.