Zn2+ modulates currents generated by the dopamine transporter: parallel effects on amphetamine-induced charge transfer and release.

The psychostimulant drug amphetamine increases extracellular monamines in the brain acting on neurotransmitter transporters, especially the dopamine transporter. Mediated by this plasmalemmal pump, amphetamine does not only induce release but also charge transfer which might be involved in the release mechanism. To study a potential link between the two phenomena, we used Zn2+ as an acute regulatory agent which modulates dopamine uptake by a direct interaction with the transporter protein. Charge transfer was investigated in patch-clamp experiments on HEK 293 cells stably expressing the human dopamine transporter, release was studied in superfusion experiments on cells preloaded with the metabolically inert transporter substrate [3H]1-methyl-4-phenylpyridinium. Ten micromoles of Zn2+ had only minor effects in the absence of amphetamine but stimulated release and inward currents induced by amphetamine depending on the concentration of the psychostimulant: the effect of 0.2 μM was not significantly modulated, whereas the effect of 1 and 10 μM amphetamine was stimulated, and the stimulation by Zn2+ was significantly stronger at 10 μM than at 1 μM amphetamine. The stimulatory action of Zn2+ on release and inward current was in contrast to its inhibitory action on dopamine uptake. This supports a release mechanism of amphetamine different from facilitated exchange diffusion but involving ion fluxes through the dopamine transporter.