TY - JOUR
T1 - Differential effects of Zn2+ on the kinetics and cocaine inhibition of dopamine transport by the human and rat dopamine transporters
AU - Bjorklund, Nicole L.
AU - Volz, Trent J.
AU - Schenk, James O.
N1 - Funding Information:
The authors would like to thank Drs. Amy Eshleman and Marc Caron for the gift of the hDAT and rDAT-expressing HEK293 cells. This work was supported by the Washington Alcohol and Drug Abuse Program (Legislative Initiative 171) to J.O.S. and N.L.B.
PY - 2007/6/22
Y1 - 2007/6/22
N2 - 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.
AB - 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.
KW - Cocaine
KW - Dopamine transporter
KW - Inductively-coupled plasma optical emission spectroscopy
KW - Pre-steady-state kinetics
KW - Rotating disk electrode voltammetry
KW - Zn modulation
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U2 - 10.1016/j.ejphar.2007.02.027
DO - 10.1016/j.ejphar.2007.02.027
M3 - Article
C2 - 17408612
AN - SCOPUS:34249294544
SN - 0014-2999
VL - 565
SP - 17
EP - 25
JO - European Journal of Pharmacology
JF - European Journal of Pharmacology
IS - 1-3
ER -