GABA dose–response curve. A, Different concentrations of GABA (as indicated) were applied for 100 msec to the same nucleated patch. The current responses were superimposed to show their different kinetic behavior. Responses to concentrations ≤100 μm were dominated by a slow rise and decay time constant. B, Amplitudes for peak and slow component from 10 patches (I_GABA) were normalized to that obtained at 1 mm GABA and were plotted semilogarithmically against the applied GABA concentrations. These data points were used to construct dose–response curves for both components. In both curves, each point represents 1–10 agonist applications. C, Before application of 1 mmGABA for 100 msec, different low GABA concentrations (as indicated) were preapplied to the patch via the control barrel of the fast application tool to predesensitize the GABA_A receptors. The current responses were superimposed to make them comparable. All data except the trace with 10 μm GABA preapplication are from the same patch. D, The data from eight nucleated patches were used for the construction of semilogarithmical dose–response plots of the current induced by 1 mm GABA (I_GABA) against the preapplied GABA concentration. The plots for peak and slow component are almost identical, i.e., there were no significant differences between the peak and the slow component regarding the GABA predesensitization. Eachpoint represents two to six experiments.