[3H]WIN 35,065-2: a ligand for cocaine receptors in striatum.
[3H]WIN 35,065-2 binding to striatal membranes was characterized, primarily by centrifugation assay. Like [3H]cocaine, [3H]WIN 35,065-2 binds to both high- and low-affinity sites. [3H]WIN 35,065-2, however, exhibits consistently higher affinities than [3H]cocaine. Saturation experiments indicate a low-affinity binding site with an apparent KD of approximately 160 nM and a Bmax of 135 fmol/mg of tissue. A high-affinity site has also been identified with an apparent KD of 5.6 nM and a Bmax of 5.2 fmol/mg of tissue. The specific-to-nonspecific binding ratios with [3H]WIN 35,065-2 were higher than with [3H]cocaine in both centrifugation and filtration assays. Pharmacological characterization suggests that [3H]WIN 35,065-2 binds to the dopamine transporter. Mazindol, GBR 12909, nomifensine, and (-)-cocaine are potent inhibitors of [3H]WIN 35,065-2 binding. In contrast, the norepinephrine transporter ligand desipramine is a weak inhibitor, and the serotonin transporter ligand citalopram does not inhibit binding. The effect of sodium on binding was examined under conditions in which (a) the low-affinity site was primarily (87%) occupied and (b) approximately 50% of both sites were occupied. The results indicate that both sites are sodium dependent. Injection of 6-hydroxydopamine into the striatum results in a significant loss of both high- and low-affinity sites, a finding suggesting that both sites are on dopaminergic nerve terminals. Taken together, these data are consistent with the presence of multiple cocaine binding sites associated with the dopamine transporter.
Ritz
M C
MC
Neuroscience Branch, NIDA Addiction Research Center, Baltimore, Maryland.
Boja
J W
JW
Grigoriadis
D
D
Zaczek
R
R
Carroll
F I
FI
Lewis
A H
AH
Kuhar
M J
MJ
D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins; D003042:Cocaine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism* / Q000473:pathology; D004298:Dopamine / Q000378:metabolism; D006892:Hydroxydopamines / Q000494:pharmacology; D008024:Ligands; D008297:Male; D016627:Oxidopamine; D051381:Rats; D011955:Receptors, Drug / Q000378:metabolism*; D014316:Tritium
D002352:Carrier Proteins; D006892:Hydroxydopamines; D008024:Ligands; D011955:Receptors, Drug; C061445:cocaine receptor; D014316:Tritium; C021278:troparil; D016627:Oxidopamine; D003042:Cocaine; D004298:Dopamine