TABLE 2.
Kinetic and equilibrium parameters for wild-type, single-mutant, and double-mutant AChRs
| AChR | τo (ms) | τc (ms) | Popen | β2 (s−1) | α2 (s−1) | θ2 | θ2 Ratio (mut/wt) | n |
|---|---|---|---|---|---|---|---|---|
| Wild-type | 0.5 ± 0.1 | 12 ± 5 | 0.04 ± 0.01 | 95 | 1910 | 0.05 | 1.0 | 10 |
| αM1-F15′L | 1.0 ± 0.2 | 0.7 ± 0.1 | 0.55 ± 0.07 | 1460 | 1150 | 1.3 | 26 | 8 |
| αM2-L11′F | 0.5 ± 0.1 | 122 ± 17 | 0.005 ± 0.001 | 10 | 2130 | 0.005 | 0.1 | 8 |
| αM1-F15′L+αM2-L11′F | 0.3 ± 0.1 | 14 ± 3 | 0.02 ± 0.01 | 80 | 4930 | 0.016 | 0.3 | 7 |
| ɛL269F (bg) | 2.3 ± 0.8 | 0.8 ± 0.3 | 0.86 ± 0.03 | 1030 | 150 | 6.9 | 138 | 3 |
| bg+αM2-L11′F | 1.7 ± 0.4 | 8.1 ± 0.3 | 0.21 ± 0.04 | 130 | 440 | 0.3 | 6 | 3 |
| bg+αM1-F15′L+αM2-L11′F | 2.2 ± 0.4 | 0.8 ± 0.1 | 0.78 ± 0.02 | 1460 | 350 | 4.2 | 84 | 3 |
The mean open (τo) and mean closed (τc) times were obtained from the corresponding histograms. Popen is the probability of channel opening within a cluster. For AChRs carrying the ɛL269F mutation, τc corresponds to the main closed component. The data correspond to the mean ± SD. Rate constants are results of a global fit of dwell times from the selected clusters at 20 mM choline by Scheme 1 (wild-type, αM1-F15′L, αM2-L11′F, and αM1-F15′L+αM2-L11′F) or by Scheme 2 for AChRs containing the background (bg) ɛL269F mutation (ɛL269F (bg), bg+αM2-L11′F, bg+αM1-F15′L+αM2-L11′F). The gating equilibrium constant, θ2, was calculated as β2/α2.