Flunitrazepam shifts the EC₅₀ for GABA to lower concentrations. A, Flunitrazepam (1 μm) was coapplied with different GABA concentrations (as indicated) to the same nucleated patch. Even concentrations as low as 100 μm GABA induced a biexponential response.B, The peak amplitudes (I_GABA) from six patches were plotted semilogarithmically against the applied GABA concentrations (+ 1 μm Flu). These data points were used to construct the sigmoidal dose–response curve. In a similar way the semilogarithmical dose–response curve of the slow component was constructed. For better comparison the original GABA dose–response relationships without flunitrazepam (control; taken from Fig.2B) are shown as dashed curves. In both curves each point represents one to six experiments. Application of 10 and 30 μm GABA yielded significantly higher responses in combination with 1 μmflunitrazepam than without (*, one-way ANOVA; p < 0.01).