Amphetamine-induced loss of human dopamine transporter activity: An internalization-dependent and cocaine-sensitive mechanism

The dopamine transporter (DAT) is a target of amphetamine (AMPH) and cocain e. These psychostimulants attenuate DAT clearance efficiency, thereby incre asing synaptic dopamine (DA) levels. Re-uptake rate is determined by the nu mber of functional transporters at the cell surface as well as by their tur nover rate. Here, we present evidence that DAT substrates, including AMPH a nd DA, cause internalization of human DAT, thereby reducing transport capac ity. Acute treatment with AMPH reduced the maximal rate of [H-3]DA uptake, decreased AMPH-induced currents, and significantly redistributed the immuno fluorescence of an epitope-tagged DAT from the plasma membrane to the cytos ol in human embryonic: kidney 293 cells. Conversely, DAT inhibitors, such a s cocaine, mazindol, and nomifensine, when administered with AMPH, blocked the reduction in [H-3]DA uptake and the redistribution of DAT immunofluores cence to the cytosol. The reductions of [H-3]DA uptake and AMPH-induced DAT internalization also were inhibited by coexpression of a dominant negative mutant of dynamin I (K44A), indicating that endocytosis modulates transpor t capacity, likely through a clathrin-mediated pathway. With this mechanism of regulation, acute application of AMPH would reduce DA uptake not only b y direct competition for uptake, but also by reducing the available cell-su rface DAT. Moreover, AMPH-induced internalization might diminish the amount of DAT available for DA efflux, thereby modulating the cytotoxic effects o f elevated extracellular DA.