Hemin enhances GABA responsiveness in cultured mouse cortical neurons. (A) Hemin (2 and 10 μM) increases the amplitude of submaximal responses to EC₂₀ concentrations of GABA in one neuron. Horizontal bars indicate GABA (short) and modulator (long) application in all figures. Scale bar, 1 nA and 4 s. (B) Concentration-response curve for hemin potentiation of the GABA response. Points (□) are plotted means ± SEM. Where not shown, errors were smaller than the size of the symbols. (C) Effects of hemin (*P < .01) and PPIX (†P < .02) on GABA responses of cultured neurons in the absence and presence of flumazenil. Error bars indicate SEM.