RELATIONSHIPS BETWEEN THE CATECHOL SUBSTRATE-BINDING SITE AND AMPHETAMINE, COCAINE, AND MAZINDOL BINDING-SITES IN A KINETIC-MODEL OF THE STRIATAL TRANSPORTER OF DOPAMINE IN-VITRO

Experiments were conducted to determine how (-)-cocaine and S(+)-amphe tamine binding sites relate to each other and to the catechol substrat e site on the striatal dopamine transporter (sDAT). In controls, m-tyr amine and S(+)-amphetamine caused release of dopamine from intracellul ar stores at concentrations greater than or equal to 12-fold those obs erved to inhibit inwardly directed sDAT activity for dopamine. In prep arations from animals pretreated with reserpine, m-tyramine and S(+)-a mphetamine caused release of preloaded dopamine at concentrations simi lar to those that inhibit inwardly directed sDAT activity. S(+)-Amphet amine and m-tyramine inhibited sDAT activity for dopamine by competing for a common binding site with dopamine and each other, suggesting th at phenethylamines are substrate analogues at the plasmalemmal sDAT. ( -)-Cocaine inhibited sDAT at a site separate from that for substrate a nalogues. This site is mutually interactive with the substrate site (K -int = 583 nM). Mazindol competitively inhibited sDAT at the substrate analogue binding site. The results with (-)-cocaine suggest that the (-)-cocaine binding site on sDAT is distinct from that of hydroxyphene thylamine substrates, reinforcing the notion that an antagonist for (- )-cocaine binding may be developed to block(-)-cocaine binding with mi nimal effects on dopamine transporter activity. However, a strategy of how to antagonize drugs of abuse acting as substrate analogues is sti ll elusive.