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 microM. 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 microM and 15.7+/-2.57 pmol/(sx10(6) 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 19.2x10(6) M-1 s-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.
Bjorklund
Nicole L
NL
School of Molecular Biosciences, Washington State University, Pullman, Washington 99164, USA.
Volz
Trent J
TJ
Schenk
James O
JO
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D003042:Cocaine / Q000494:pharmacology*; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000037:antagonists & inhibitors*; D006801:Humans; D007700:Kinetics; D008297:Male; D010396:Penicillamine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015032:Zinc / Q000494:pharmacology*
D050483:Dopamine Plasma Membrane Transport Proteins; D010396:Penicillamine; D003042:Cocaine; D015032:Zinc; D004298:Dopamine