Table II.
Kinetic Parameters for AChRs Containing Wild-type or Mutant α Subunits
| k − | k + | K/μM | β1 | α1 | Θ1 | β2 | α2 | Θ2 | k +block | k −block | K B/mM | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wild type | ||||||||||||||||||||||||
| scheme SI | 21,900 | 129 | 170 | 216 | 3,320 | 6.5E-2 | 48,900 | 1,660 | 29.5 | 9.67 | 74,100 | 7.67 | ||||||||||||
| (±438) | (±2) | (±21) | (±350) | (±3,960) | (±21) | (±0.71) | (±3,370) | |||||||||||||||||
| scheme SII | 21,900 | 129 | 170 | 216 | 3,320 | 6.5E-2 | 48,900 | 1,660 | 29.5 | 9.67 | 74,100 | 7.67 | ||||||||||||
| (±3,140) | (±23) | (±21) | (±220) | (±3,960) | (±157) | (±0.67) | (±3,120) | |||||||||||||||||
| αN217K | ||||||||||||||||||||||||
| scheme SI | 1,890 | 116 | 16.2 | 72.4 | 7,640 | 9.5E-3 | 31,400 | 873 | 35.9 | 10.7 | 74,530 | 7.0 | ||||||||||||
| (±35) | (±1.7) | (±2.8) | (±390) | (±350) | (±9.8) | (±1.1) | (±4,740) | |||||||||||||||||
| scheme SII | 1,838 | 115 | 16.0 | 70.6 | 7,700 | 9.2E-3 | 28,500 | 816 | 34.8 | 13.2 | 78,800 | 6.0 | ||||||||||||
| (±52) | (±1.6) | (±2.5) | (±360) | (±4,700) | (±32) | (±0.8) | (±4,760) | |||||||||||||||||
| αN217Q | ||||||||||||||||||||||||
| scheme SI | 26,300 | 128 | 205 | 106 | 7,370 | 1.4E-2 | 61,700 | 2,300 | 27 | 8.8 | 57,700 | 6.6 | ||||||||||||
| (±610) | (±2.3) | (±13.4) | (±910) | (±3,100) | (±36) | (±0.54) | (±2,620) | |||||||||||||||||
| scheme SII | 26,300 | 127 | 207 | 107 | 7,380 | 1.4E-2 | 61,700 | 2330 | 27 | 8.8 | 57,700 | 6.6 | ||||||||||||
| (±1130) | (±2.2) | (±9.4) | (±700) | (±3100) | (±250) | (±0.6) | (±5,940) | |||||||||||||||||
| αN217E | ||||||||||||||||||||||||
| scheme SI | 25,600 | 77.9 | 328 | 91.6 | 4,560 | 2.0E-2 | 55,600 | 1,507 | 37 | 14.0 | 74,000 | 5.3 | ||||||||||||
| (±550) | (±1.3) | (±9.0) | (±570) | (±930) | (±20) | (±0.6) | (±1,730) | |||||||||||||||||
| scheme SII | 23,300 | 72.3 | 320 | 96.9 | 457 | 2.1E-1 | 55,600 | 1,770 | 31 | 13.9 | 76,400 | 5.5 | ||||||||||||
| (±580) | (±1.2) | (±8.0) | (±19) | (±930) | (±140) | (±0.7) | (±5,990) |
Rate constants are as defined in schemes i and ii (left column, see text), in units of μM−1 s−1 for association rate constants, and s−1 for all others. Values are results of a global fit of each scheme to data obtained over a range of ACh concentrations, with standard errors in parenthesis (see methods). Channel open equilibrium constants, Θ, are ratios of the corresponding opening to closing rate constants, β/α. Association and dissociation rate constants are presented on a per site basis because of the constraint of equivalent binding sites (see text). In all but one case, the fitting was carried out with the value of β2 fixed to that obtained from analysis of data obtained at low ACh concentrations (Table III); the exception was the fit of scheme SI to the αN217K data where the value of β2 from the global fit was essentially the same as that obtained at low ACh concentrations.