A, current traces after subtraction of the corresponding records in the presence of 30 μm SKF89976A. Aa, an oocyte expressing WT rGAT1 and Ab another oocyte expressing the mutated form. B, normalized Q–V curves obtained from integration of transients such as those in A (□, wild-type, n = 27; ○, K448E, n = 25; four different batches). Curves in B were fitted with a Boltzmann distribution to give the parameters in the text. C, relation between transport-associated current (at −120 mV) and Qmax for oocytes expressing wild-type rGAT1 (□ and continuous line) and oocytes expressing the K448E form (○ and dashed line).