The β3 N265M mutation prevents potentiation by F6. A. Concentration-response relationship. The mutant α5β3(N265M)γ2L receptors are less sensitive to GABA than the wild type (EC50 = 23.6 μM, slope = 0.71, n = 8) (mean ± S.E.M). B. In contrast to the wild type, F6 failed to enhance responses to 3 μM GABA (EC20, bottom), and slightly reduced responses to 1 mM GABA (top).