Differential effects of Zn2+ on the kinetics and cocaine inhibition of dopamine transport by the human and rat dopamine transporters

Zn2+ may play a major role in the modulation of neurotransmission because it modulates membrane receptors and channels. Recent literature has shown Zn2+ inhibits dopamine transport by the dopamine transporter (DAT), the main target of cocaine and some other drugs of abuse. Cocaine inhibits DAT and modulation of the DAT by Zn2+ may alter effects of cocaine on dopamine neurotransmission. This study investigates how Zn2+ changes DAT kinetics and its inhibition by cocaine. Steady-state and pre-steady-state kinetics of DAT activity were investigated using rotating disk electrode voltammetry. Values of KM and Vmax in hDAT and effects of cocaine match those in the literature. Zn2+ allosterically inhibited transport in the human DAT (hDAT) with a KI = 7.9 ± 0.42 μM. Removal of endogenous Zn2+ with penicillamine in hDAT increased transport values. In contrast, Zn2+ did not alter transport by rat DAT (rDAT), with KM and Vmax values of 1.2 ± 0.49 μM and 15.7 ± 2.57 pmol/(s × 106 cells), respectively, and removal of Zn2+ did not increase dopamine transport values. Zn2+ allosterically reduced the inhibition by cocaine in hDAT. Results of pre-steady-state studies demonstrated that Zn2+ increases the second order binding rate constant for dopamine to hDAT (3.5 fold to 19.2 × 106 M− 1s− 1 for hDAT). In rat striatal homogenates Zn2+ increased initial dopamine transport velocity and decreased cocaine inhibition providing evidence for differences in sensitivity to Zn2+ between the three different preparations. Modulation of the DAT by Zn2+ needs to be assessed further in development of cocaine antagonists.