Table 1. Gating rate and equilibrium constants.
| Construct | Opening rate constant β, S-1 | Closing rate constant αB, S-1 | Corrected α, S-1 | iO, pA | iB, pA | KB, mM | Gating equilibrium constant, Θ, uncorrected/corrected | Θ ratio, mut/WT | N |
|---|---|---|---|---|---|---|---|---|---|
| WT | 121 | 834 | 2,583 | 7.0 | 2.3 | 9.5 | 0.15/0.05 | 1 | 4 |
| α9′AHyb 2 | 566 | 29.2 | 91.8 | 8.2 | 2.6 | 9.3 | 19.4/6.2 | 124 | 4 |
| α9′AHyb 1 | 131 | 14.9 | 64.1 | 8.2 | 1.9 | 6.1 | 8.8/2.0 | 40 | 4 |
| α9′TDbl | 472 | 17.7 | 31.8 | 7.0 | 3.9 | 25.2 | 26.7/14.8 | 296 | 3 |
| α9′THyb 2 | 310 | 202 | 420 | 7.0 | 3.4 | 18.6 | 1.5/0.74 | 14.8 | 6 |
| α9′THyb 1 | 134 | 59.1 | 155 | 7.0 | 2.7 | 12.3 | 2.3/0.86 | 17.2 | 6 |
| α9′TOut | 569 | 83.7 | — | — | — | — | 6.8 | — | 3 |
| α9′MDbl | 414 | 47.7 | 118 | 7.2 | 3.0 | 14.3 | 8.7/3.5 | 70 | 3 |
| α9′MHyb 2 | 232 | 231 | 664 | 7.2 | 2.5 | 10.6 | 1.0/0.35 | 7.0 | 4 |
| α9′MHyb 1 | 121 | 73.3 | 245 | 7.2 | 2.2 | 8.5 | 1.7/0.49 | 9.8 | 4 |
| α9′MOut | 332 | 289 | — | — | — | — | 1.1 | — | 1 |
| α9′CDbl | 339 | 47 | 136 | 7.8 | 2.7 | 10.6 | 7.2/2.5 | 50 | 3 |
| α9′COut | 359 | 150 | — | — | — | — | 2.4 | — | 3 |
| α9′VDbl | 69 | 930 | 3,408 | 6.6 | 1.8 | 7.5 | 0.07/0.02 | 0.4 | 2 |
| α9′IDbl | 147 | 1247 | 3,897 | 5.0 | 1.6 | 9.4 | 0.12/0.04 | 0.8 | 4 |
| α17′ADbl | 1,291 | 687 | — | — | — | — | 1.9 | 12.7 | 4 |
| α17′DDbl | 1,683 | 149 | — | — | — | — | 11.3 | 75.3 | 6 |
| α17′GDbl | 1,357 | 1,105 | — | — | — | — | 1.2 | 8 | 3 |
| α17′SDbl | 2,041 | 814 | — | — | — | — | 2.5 | 16.7 | 4 |
| α17′TDbl | 202 | 404 | — | — | — | — | 0.5 | 3.3 | 2 |
| α17′YDbl | 1,109 | 164 | — | — | — | — | 6.8 | 45.3 | 3 |
| α27′IDbl | 2,396 | 139 | — | — | — | — | 17.2 | 115 | 4 |
| α27′IHyb | 627 | 401 | — | — | — | — | 1.6 | 10.7 | 4 |
| ε9′A | 563 | 53 | 232 | 7.0 | 1.6 | 5.9 | 10.6/2.4 | 48 | 3 |
| ε9′M | 337 | 81.7 | 318 | 7.0 | 1.8 | 6.9 | 4.1/1.1 | 22 | 2 |
| β9′M | 547 | 111 | 472 | 6.8 | 1.6 | 6.3 | 4.9/1.2 | 24 | 1 |
| β9′N | 622 | 86 | 356 | 6.5 | 1.6 | 7.2 | 7.2/1.7 | 34 | 2 |
The rate constants were obtained from single-channel currents elicited by 20 mM choline. The apparent closing rate constant, αB, is slower than the value at low choline concentrations because of channel block by the agonist. iO and iB are the open-channel current amplitudes at 200 μM choline (negligible channel block) and 20 mM choline, respectively. KB denotes the calculated value of the equilibrium dissociation constant for channel block by choline at — 100 mV (see Methods). For the Ala double mutant, KB was 16.6 mM. The subscript “Out” refers to parameters measured at a depolarized membrane potential (+60 mV; see Fig. 7). A closing rate constant corrected for channel-block (α) was calculated for all 9′ constructs (see Methods). The rate constants are means, and N is the number of patches.