Impact of 1,500 μM CPM-acid on the γ-aminobutyric acid (GABA) concentration-response relationship. Each symbol is the mean ± SD derived from five different oocytes. The curves are nonlinear least square fits of the two datasets to equation 1 (see Data Analysis section), with the minimum constrained to 0% (i.e., no current in the absence of GABA). These fits yielded GABA EC₅₀s of 44 μM (95% CI, 35 to 54 μM) in the absence of CPM-acid and 45 μM (95% CI, 32 to 62 μM) in the presence of CPM-acid (P = 0.9148). The maximal peak current amplitudes were 104% (95% CI, 99 to 108%) in the absence of CPM-acid and 64% (95% CI, 60 to 69%) in the presence of CPM-acid (P < 0.0001) with identical slopes of 1.3 (95% CIs, 1.0 to 1.6 and 0.8 to 1.8, respective).