[3H]GBR-12935 binding sites in human striatal membranes: binding characteristics and changes in parkinsonians and...

The binding of the diphenyl-substituted piperazine derivative, [3H]GBR-12935, a selective dopamine uptake inhibitor, to the post-mortem human putamen was studied. Inhibition curves by dopamine uptake inhibitors suggested the existence of two populations of [3H]GBR-12935 binding sites: one is potently inhibited by mazindol and/or nomifensine, and the second binding site is benztropine- and/or GBR 12909-sensitive. In the human putamen, [3H]GBR-12935 labeled both these two distinct binding sites. The [3H]GBR-12935 binding displaced by mazindol was enriched in the mouse and rat striatum, but not in the cultured mouse neuroblastoma cell N1E-115. The mazindol-sensitive [3H]GBR-12935 binding site increased in the presence of sodium and markedly decreased in the putamen from parkinsonians (45% of controls). On the other hand, the [3H]GBR-12935 binding displaced by benztropine showed no sodium-dependent increase and was not decreased in the putamen from parkinsonians. In the putamen from schizophrenics, the [3H]GBR-12935 binding did not significantly change in the density, while that displaced by mazindol tended to increase. It is concluded that in the human putamen, [3H]GBR-12935 binds to two distinct sites. One site is partially sodium-dependent and appears to be associated with a high-affinity dopamine uptake system on dopaminergic nerve terminals. The second binding site shows no sodium-dependency and may be associated with a nondopaminergic and/or extraneuronal DA uptake system.