The dopamine (DA) transporter (DAT) mediates the removal of released DA. DAT is the major molecular target responsible for the rewarding properties and abuse potential of the psychostimulant amphetamine (AMPH). AMPH has been shown to reduce the number of DATs at the cell surface, and this AMPHinduced cell surface DAT redistribution may result in longlasting changes in DA homeostasis. The molecular mechanism by which AMPH induces trafficking is not clear. Because AMPH is a substrate, we do not know whether extracellular AMPH stimulates trafficking through its interaction with DAT and subsequent alteration in DAT function, thereby triggering intracellular signaling or whether AMPH must be transported and then act intracellularly. In agreement with our previous studies, extracellular AMPH caused cytosolic redistribution of the wildtype human DAT (WT-hDAT). However, AMPH did not induce cytosolic redistribution in an uptake-impaired hDAT (Y335A-hDAT) that still binds AMPH. The divalent cation zinc (Zn 2Ļ© ) inhibits WT-hDAT activity, but it restores Y335A-hDAT uptake. Coadministration of Zn 2Ļ© and AMPH consistently reduced WThDAT trafficking but stimulated cytosolic redistribution of Y335A-hDAT. Furthermore, direct intracellular application of AMPH, via a whole-cell patch pipette, stimulated the trafficking of Y335A-hDAT. Taken together, these data suggest that the DAT transport cycle is not required for AMPH-induced downregulation and that an increase of intracellular AMPH is an essential component of DAT redistribution. Dopamine (DA) is a monoaminergic neurotransmitter involved in the control of locomotion, cognition, reward, and emotion (Iversen, 1971;Giros and Caron, 1993). The DA transporter (DAT) coordinates the spatial and temporal regulation of dopaminergic neurotransmission by mediating the reuptake of DA into presynaptic neurons. Although diffusion and enzymatic degradation contribute to reducing the synaptic concentration of DA, knockout studies have established DAT as the primary mechanism controlling extracellular DA levels (Giros et al., 1996;Jones et al., 1998). The regulatory mechanisms governing DAT are critical to DA signaling/ homeostasis. Altered dopaminergic signaling has been implicated in multiple brain disorders, including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and addiction (Jucaite, 2002).DAT belongs to the Na Ļ© /Cl ĻŖ -dependent transporter gene family, which also consists of plasmalemmal carriers for the other monoamines, norepinephrine, epinephrine, and serotonin. Modulation of transporter surface expression may constitute a dynamic component of DA clearance (Melikian and Buckley, 1999;Loder and Melikian, 2003;Sorkina et al., 2005). Indeed, the clearance efficiency of DAT is determined not only by the transport rate of an individual transporter but also by the number of functional transporters on the cell surface. DAT trafficking has been shown to be regulated by receptor signaling, as well as by direct activation of protein