Figure 1.
The mutationβ_{2}-R207C increases both the rate of deactivation and GABA EC_{50} but does not affect desensitization. *A, B*, α_{1}β_{2} or α_{1}β_{2}-R207C receptors were challenged with 2 msec (*A*) or 1 sec(*B*) pulses of GABA. All traces are peak normalized. Peak currents of traces shown varied between 65 and 150 pA. Because of differences in EC_{50}, GABAconcentrations used on wild-type and R207C-containing receptors were 10 and 100 mm, respectively. Each trace is the average of between 25 and 200 sweeps, recorded while the patches were held at –60 mV. The top traces in both panels are recordings from open electrode tips made at the end of each experiment to evaluate the speed of solution exchange. *C*, GABA concentration–response curves for wild-type (solid lines, squares) and mutant (dashed lines, circles) receptors for 1 sec GABA pulses. The filled symbols show data generated by measuring peak GABA currents, and the open symbols show data from currents measured 500 msec after GABA application. The curves were generated by fitting the data with the equation *I*_{GABA}/*I*_{GABA-max} = *Y*_{max}/(1 + 10^(logEC_{50} – log[GABA])^*N*), where *N* is the Hill coefficient, using Prism software (GraphPad Software, San Diego, CA). EC_{50} and Hill coefficient values were: 14μm, 0.6 (wild-type peak); 0.7 μm, 0.6 (wild type, 500 msec); 561 μm, 1.2 (mutant peak); and 240 μm, 1.6 (mutant, 500 msec). All EC_{50} values were significantly different from each other except for the mutant at peak and mutant at 500 msec, which had overlapping 95% confidence intervals (generated by fitting software). All Hill coefficients had overlapping 95% confidence intervals.