EVIDENCE THAT PURE UPTAKE INHIBITORS INCLUDING COCAINE INTERACT SLOWLY WITH THE DOPAMINE NEURONAL CARRIER

We have studied the ability of various uptake blockers to protect the dopamine neuronal carrier labeled with [H-3]GBR 12783 ethoxy)ethyl]-4- (3-phenyl-2-(propenyl)-piperazine} against N-ethylmaleimide-induced al kylation, using membrane preparations obtained from rat striatum. Pure uptake inhibitors such as mazindol, pyrovalerone, nomifensine and met hylphenidate, and substrates (dopamine, d-amphetamine, m-tyramine) pro tected the [3H]GBR 12783 binding site in a concentration-dependent man ner. Preincubation of the membranes with these agents prior to N-ethyl maleimide treatment did not modify the protecting ability of substrate s, whereas it significantly improved that of pure uptake inhibitors in cluding cocaine. When the preincubation was omitted, the concentration dependence of the protection observed with pure uptake inhibitors dec reased and a maximal 40% protection was observed for 10 mu M to 1 mM c ocaine concentrations. Effective protecting concentrations of blockers are correlated with their K-i determined in standard binding studies. These results reveal that all pure uptake inhibitors bind slowly to t he dopamine neuronal carrier whereas substrates interact with it rapid ly.