The present address of Dr. S. L. Povlock is The Vollum Institute, Oregon Health Sciences University, L474, 3181 S.W. Sam Jackson Road, Portland, OR 97201-3098, U.S.A.
A Multisubstrate Kinetic Mechanism of Dopamine Transport in the Nucleus Accumbens and Its Inhibition by Cocaine
Article first published online: 18 NOV 2002
Journal of Neurochemistry
Volume 69, Issue 3, pages 1093–1105, September 1997
How to Cite
Povlock, S. L. and Schenk, J. O. (1997), A Multisubstrate Kinetic Mechanism of Dopamine Transport in the Nucleus Accumbens and Its Inhibition by Cocaine. Journal of Neurochemistry, 69: 1093–1105. doi: 10.1046/j.1471-4159.1997.69031093.x
- Issue published online: 18 NOV 2002
- Article first published online: 18 NOV 2002
- Received February 10, 1997; revised manuscript received April 24, 1997; accepted April 25, 1997.
- GBR 12909;
- Inhibition of transport;
- Nucleus accumbens;
- Rotating disk voltammetry;
- Kinetic mechanism of transport
Abstract: Kinetic studies of dopamine transport into suspensions of nucleus accumbens (NAcc) and effects of Na+ and Cl− as cosubstrates were performed using rotating disk electrode voltammetry. To mimic chemical neurotransmission, dopamine was added as a rapid pulse, and transporter-mediated clearance of dopamine was evaluated kinetically. This paradigm was shown to approximate a zero trans entry transport experiment. Dopamine was taken up with apparent Km and Vmax values of 1.3 µM and 375 pmol/s/g wet weight, respectively. Transport exhibited apparent trans acceleration. Substitution of Na+ with choline or Cl− with isethionate reduced dopamine transport with reaction orders of two and unity, respectively, accompanied by reductions in Vmax with no changes in Km. Apparent KNa and KCl values were 70.0 and 92.1 mM, respectively. Dopamine transport in NAcc was found to follow a partially random, sequential mechanism in which dopamine and Na+ bind randomly to the transporter followed by binding of Cl− before transport. Cocaine inhibited dopamine transport and the influences of the other substrates allosterically with an overall Ki of 0.30 µM. Thus, the general kinetic mechanism of the transport of dopamine in the NAcc is identical to that previously reported by this laboratory for dopamine transport in the striatum. However, the dopamine transporter in the NAcc is more tightly regulated by Na+, possesses a higher kinetic turnover rate, is four times more sensitive to cocaine than the striatal transporter, and exhibits cocaine inhibition independent of [substrate]. These findings suggest that cocaine modulates chemical signaling in NAcc differently than in striatum, providing down-regulation of function irrespective of [substrate], thereby enhancing dopaminergic signaling more robustly in the NAcc than in the striatum.
Abbreviations used: [Cl−]o, extracellular Cl− concentration; [DA]o, extracellular dopamine concentration; [Na+]o, extracellular Na+ concentration; NAcc, nucleus accumbens; RDE, rotating disk electrode; SER, standard error of regression.