Table 1.
Current kinetic properties of untethered GABAA receptors
|
|
Activation 10-90% (msec) |
Desensitization |
Deactivation |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Construct (n) |
τ1 (msec) |
τ2 (msec) |
%A1 |
%A2 |
%C |
τweight (msec) |
|||||
| WT (5) |
4.0 ± 0.8 |
19.5 ± 0.9 |
232.5 ± 32.9 |
17 ± 3 |
29 ± 3 |
54 ± 5 |
267 ± 50 |
||||
| Het (5) |
4.5 ± 0.5 |
14.8 ± 1.1 |
181.2 ± 14.6 |
20 ± 1 |
35 ± 1 |
46 ± 2 |
147 ± 10a
|
||||
| Hom (5,3) |
53.9 ± 4.7a,b
|
NA |
NA |
07a,b
|
07a,b
|
1007a,b
|
31 ± 5a,b
|
||||
Current kinetic parameters were obtained from wild-type (WT), heterozygous mutant (Het), and homozygous mutant (Hom) transfections during a 400 msec step into 1 mm GABA. Activation time, weighted deactivation time (τweight), and the desensitization fast (τ1) and intermediate (τ2) time constants as well as the percentage components of fast (%A1), intermediate (%A2), and residual (%C) desensitization were calculated as described in Materials and Methods. Each of the five cells expressing homozygous mutant receptors included in the analysis lacked fast and intermediate components of desensitization. Because only three of the cells expressing homozygous mutant receptors had peak currents >100 pA, only currents from these cells were fit for activation and deactivation times, each of which were significantly different from both wild-type and heterozygous currents. The deactivation of heterozygous receptor currents was significantly faster than that of wild-type currents, but there was no difference in current activation or desensitization.
Statistically different from wild type.
Statistically different from heterozygous.