Channel properties of adult- and embryonic-type AChR carrying mutations in the α subunit M4 segment
| α Subunit | τon | τburst | n/b | Current | n |
|---|---|---|---|---|---|
| msec | pA | ||||
| Adult (ɛ-containing) AChR | |||||
| Wild-type | 0.98 ± 0.23 | 1.25 ± 0.19 | 1.08 ± 0.10 | 5.70 ± 0.30 | 6 |
| M4×4 | 0.23 ± 0.021-a | 0.29 ± 0.101-a | 1.09 ± 0.05 | 5.50 ± 0.20 | 6 |
| L411A | 0.93 ± 0.16 | 1.06 ± 0.15 | 1.12 ± 0.10 | 5.60 ± 0.10 | 5 |
| M415A | 1.30 ± 0.25 | 1.49 ± 0.21 | 1.10 ± 0.02 | 5.80 ± 0.12 | 3 |
| C418A | 0.31 ± 0.071-a | 0.36 ± 0.071-a | 1.03 ± 0.02 | 5.80 ± 0.10 | 5 |
| T422A | 0.18 ± 0.031-a | 0.20 ± 0.041-a | 1.04 ± 0.03 | 5.70 ± 0.24 | 6 |
| F414A | 1.34 ± 0.30 | 1.49 ± 0.40 | 1.08 ± 0.06 | 5.80 ± 0.25 | 8 |
| Embryonic (γ-containing) AChR | |||||
| Wild-type | 5.51 ± 0.51 | 9.20 ± 1.41 | 1.70 ± 0.14 | 3.85 ± 0.13 | 6 |
| C418A | 2.82 ± 0.561-a | 4.03 ± 0.901-a | 1.28 ± 0.10 | 3.67 ± 0.14 | 6 |
| T422A | 1.55 ± 0.031-a | 1.80 ± 0.051-a | 1.20 ± 0.10 | 4.00 ± 0.20 | 6 |
Recordings were obtained at a membrane potential of −70 mV from HEK cells transfected with α (wild-type or mutants), β, δ, and either ɛ or γ subunit cDNAs. Values for the mean open time (τon) and mean burst duration (τburst) were obtained from the corresponding open-time histograms and correspond to the major component (relative area > 0.80). A burst was defined as a series of opening events separated by <1 msec. n/b is the number of openings per burst. In the case of αM4×4, 50% of the open-time histograms showed a minor component (relative area, 0.14 ± 0.04) of 1.09 ± 0.32 msec. A minor component of 1.03 ± 0.16 msec (relative area, 0.20 ± 0.03) was observed in 40% of the recordings from C418A-containing channels. In all recordings corresponding to αT422A-containing AChRs, open-time histograms were well fitted by only one component.
↵1-a Statistically different from the wild-type value (p < 0.001).