The effect of three tricyclic antidepressants imipramine, desipramine and clomipramine (TCAs) and two serotonin selective reuptake inhibitors fluoxetine and paroxetine (SSRIs) on the activity of the GABA transporter rGAT WT and on the lysine 448 glutamate mutant have been studied with electrophysiological and confocal microscopy experiments on Xenopus oocytes transfected with the transporters' cRNAs. The drugs were applied to the two transporter forms and their effects were compared. Lysine 448 of rGAT corresponds to aspartate 401 of the bacterial leucine transporter LeuTAa, a residue that has been identified in the TCA binding pocket. The drugs application seems to have no effect on the pre-steady state and uncoupled current. While two of the three tested TCAs clomipramine and imipramine and the SSRIs progressively inhibit with the same efficacy the GABA associated currents in both forms of transporters, desipramine causes a stronger block of the transport associated current of the rGAT K448E mutant. The results show that the residue at position 448 of rGAT plays a fundamental role in the antidepressant interaction. Besides, in order to clarify the apparently conflicting results about competitive and non competitive inhibition, the effect of desipramine at different GABA concentration has been investigated revealing that the application of the drug at IC₅₀ concentration change both I_max and K_m. These results are consistent with the three-dimensional model that suggests two different binding sites for drug and substrate, and let to hypothesize that the presence of TCAs will block the access of the substrate to the binding site.