Table 4.
Kinetic parameters of other mutants of the α1 GlyRa
| Construct | τdeactivation (ms) | τentry into desensitization (ms) | τrecovery from desensitization (s) |
|---|---|---|---|
| Wild type | 3.95 ± 0.48 (0.544 ± 0.036) | 4.92 ± 1.08 (0.448 ± 0.044) | 2.80 ± 0.27 |
| 28.8 ± 3.5 | 100 ± 22 (0.274 ± 0.045) | ||
| (21/29) | 1380 ± 420 (0.278 ± 0.030) | ||
| (15/38) | |||
| G4′C | 1.66 ± 0.37 | 11.1 ± 3.6 | — |
| (5/9) | (5/9) | ||
| K24′A | 1.36 ± 0.22 | 2320 ± 693 | 0.281 ± 0.038 |
| (14/14) | C = 0.41 ± 0.05 | ||
| (9/15) | |||
| K24′A + | 3.3 ± 0.42 | 1650 ± 940 (0.498 ± 0.046) | 0.227 ± 0.046 |
| A–3′T | (7/7) | 21,700 ± 8700 (0.278 ± 0.053) | |
| C = 0.22 ± 0.08 | |||
| (4/10) | |||
| GlyRM3M4 311S | 4.91 ± 0.64 (0.451 ± 0.036) | 9.34 ± 2.24 (0.321 ± 0.087) | 2.05 ± 0.23 |
| 28.0 ± 3.3 | 165 ± 44 (0.328 ± 0.091) | ||
| (16/18) | 1130 ± 390 (0.352 ± 0.076) | ||
| (8/20) | |||
| GlyRM3M4 311A | 4.28 ± 0.79 (0.394 ± 0.046) | 7.52 ± 1.84 (0.293 ± 0.048) | 2.03 ± 0.12 |
| 23.8 ± 1.8 | 86.8 ± 21.4 (0.374 ± 0.050) | ||
| (12/15) | 492 ± 128 (0.334 ± 0.073) | ||
| (8/17) | |||
| GlyRM3M4 311H | 7.07 ± 0.73 | 7.24 ± 1.18 (0.406 ± 0.031) | 2.02 ± 0.23 |
| (9/18) | 68.7 ± 9.2 | ||
| (10/19) | |||
| H311S | 5.08 ± 1.34 (0.515 ± 0.063) | 7.12 ± 3.06 (0.286 ± 0.035) | 1.80 ± 0.14 |
| 17.2 ± 3.1 | 45.8 ± 16.0 (0.335 ± 0.021) | ||
| (6/9) | 240 ± 78 (0.334 ± 0.073) | ||
| (5/9) | |||
| GlyRM3M4 8xAla | 16.0 ± 5.56 (0.686 ± 0.037) | 28.0 ± 17.7 (0.592 ± 0.0075) | 0.702 ± 0.076 |
| 96.4 ± 27.9 | 166 ± 83 (0.181 ± 0.025) | ||
| (6/13) | 8210 ± 4570 (0.227 ± 0.065) (6/10) | ||
| GlyRM3M4 311H + K24′A | 1.09 ± 0.24 | 109 ± 22 (0.565 ± 0.105) | 0.164 ± 0.030 |
| (4/6) | 2490 ± 1540 | ||
| (5/6) | |||
| GlyRM3M4 8xAla + G4′C | 1.08 ± 0.18 | 2.10 ± 0.25 | — |
| (7/7) | (8/8) |
aAll errors are SEs. The fractions in parentheses have the same meaning as in Tables 2 and 3. Unlike all other tested mutants, the two constructs containing the GlyR α1 K24′A mutation exhibited desensitization time courses that seemed to reach a non-zero current level at steady state, as judged from the channel's sustained currents at the end of 1 minute applications of saturating Gly. Steady-state current levels were normalized to their time courses' peak amplitude values to allow averaging across patches; these average values are presented in the table as “C.” The α1 GlyR G4′C mutant exhibited an unusually fast, and apparently irreversible, rundown in the outside-out configuration. As a result, it was not possible to determine its rate of recovery from desensitization. Because of its poor functional expression, it was also not possible to quantify the rate of recovery from desensitization of the α1 GlyRM3M4 8xAla + G4′C construct. Each time course was obtained from a different patch of membrane. —, Not applicable.