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(+)-amphetamine binding sites relate to each other and to the catechol substrate site on the striatal dopamine transporter (sDAT). In controls, m-tyramine and S(+)-amphetamine caused release of dopamine from intracellular stores at concentrations > or = 12-fold those observed to inhibit inwardly directed sDAT activity for dopamine. In preparations from animals pretreated with reserpine, m-tyramine and S(+)-amphetamine caused release of preloaded dopamine at concentrations similar to those that inhibit inwardly directed sDAT activity. S(+)-Amphetamine and m-tyramine inhibited sDAT activity for dopamine by competing for a common binding site with dopamine and each other, suggesting that phenethylamines are substrate analogues at the plasmalemmal sDAT. (-)-Cocaine inhibited sDAT at a site separate from that for substrate analogues. 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 hydroxyphenethylamine substrates, reinforcing the notion that an antagonist for (-)-cocaine binding may be developed to block (-)-cocaine binding with minimal effects on dopamine transporter activity. However, a strategy of how to antagonize drugs of abuse acting as substrate analogues is still elusive.
Wayment
H
H
Department of Chemistry, Washington State University, Pullman 99164-4630, USA.
Meiergerd
S M
SM
Schenk
J O
JO
D000661:Amphetamine / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D002396:Catechols / Q000378:metabolism*; D003042:Cocaine / Q000378:metabolism*; D003342:Corpus Striatum / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins; D007700:Kinetics; D008297:Male; D008454:Mazindol / Q000378:metabolism*; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008954:Models, Biological; D009419:Nerve Tissue Proteins; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity; D014439:Tyramine / Q000378:metabolism
D002352:Carrier Proteins; D002396:Catechols; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D008454:Mazindol; D000661:Amphetamine; D003042:Cocaine; C028169:3-tyramine; D014439:Tyramine