[3H] cocaine labels a binding site associated with the serotonin transporter in guinea pig brain: allosteric modulation by paroxetine.
We studied the characteristics of [3H]cocaine binding to membranes prepared from whole guinea pig brain. Cocaine binding was specific and saturable. A one-site binding model fit the data adequately: the Kd value of [3H]cocaine was 44 nM with a Bmax value of 280 fmol/mg protein. The rank order of potency for the [3H]cocaine binding site was paroxetine > clomipramine > (-)-cocaine > fluoxetine > mazindol > desipramine > GBR12909 > phencyclidine > benztropine > GBR12935 > (+)-cocaine. The IC50 values of these drugs for inhibition of [3H]cocaine binding were highly correlated with their IC50 values for inhibition of [3H]5-HT uptake into synaptosomes prepared from whole guinea pig brain. High affinity 5-HT uptake inhibitors produced dose-dependent wash-resistant (pseudoirreversible) inhibition of [3H]cocaine binding. The wash-resistant inhibition produced by paroxetine was due to an increase in the Kd of [3H]cocaine binding sites, and was accompanied by an increase in the dissociation rate, consistent with an allosteric mechanism. These studies suggest that, using membranes prepared from whole guinea pig brain, [3H]cocaine labels a binding site associated with serotonin transporter and that paroxetine and cocaine bind to different sites on the serotonin transporter.
Akunne
H C
HC
Laboratory of Clinical Psychopharmacology, NIDA Addiction Research Center, Baltimore, MD 21224.
de Costa
B R
BR
Jacobson
A E
AE
Rice
K C
KC
Rothman
R B
RB
D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003042:Cocaine / Q000378:metabolism*; D006168:Guinea Pigs; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D017374:Paroxetine / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins; D013574:Synaptosomes / Q000378:metabolism; D014316:Tritium
D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D010879:Piperazines; D050486:Serotonin Plasma Membrane Transport Proteins; D014316:Tritium; D012701:Serotonin; D017374:Paroxetine; C043425:vanoxerine; D003042:Cocaine