High-affinity [ 3H]GBR 12783 binding to a specific site associated with the neuronal dopamine uptake complex in the central nervous system

Abstract

We labelled the neuronal dopamine uptake system by using the potent dopamine uptake inhibitor GBR 12783 in its tritiated form (18.3 Ci/mmol). The binding of [ 3H]GBR 12783 to rat striatal membranes was saturable and specific with a K d of 1.6 nM and a B max of 10.3 pmol · mg protein −1 as determined by Scatchard analysis. [ 3H]GBR 12783 binding to rat striatal membranes was inhibited by dopamine uptake inhibitors with IC 50 highly correlated with their IC 50 for inhibiting [ 3H]dopamine uptake by a rat striatal synaptosomal preparation. The rank order of potency was the following: GBR 12783 > amfonelic acid > mazindol > pyrovalerone > nomifensine > benztropine > amineptine > methylphenidate > cocaine. Substrates of dopamine uptake competed with [ 3H]GBR 12783 binding at concentrations higher than those at which they inhibited [ 3H]dopamine uptake. In rats with a unilateral section of the medial forebrain bundle, the decrease in [ 3H]GBR 12783 binding to membranes prepared from the ipsilateral striatum was equal to the decrease in [ 3H]dopamine uptake by a synaptosomal preparation obtained from the same striatum. [ 3H]GBR 12783 bound in a sodium-dependent manner to membranes prepared from striatum, nucleus accumbens and tuberculum olfactorium. GBR 12783 displayed an approximately 150-fold lower affinity for the cortical norepinephrine uptake system labelled with [ 3H]desipramine than for the dopamine transport complex labelled with [ 3H]GBR 12783. [ 3H]GBR 12783 appears an attractive tool for the selective characterization of the dopamine uptake system in vitro.