Cocaine and GBR 12783 recognize nonidentical, overlapping binding domains on the dopamine neuronal carrier.
In incubation medium containing Na+ as the only cation, the specific binding of [3H]cocaine to a membrane preparation obtained from rat striatum reached a maximal level for 10 mM Na+, whereas higher concentrations decreased its affinity. The specific binding of [3H]cocaine was inhibited monophasically by GBR 12783, mazindol, nomifensine and substrates of the transporter; in saturation experiments, GBR 12783 competitively blocked the [3H]cocaine specific binding and vice versa. Treatment of the striatal membranes with N-ethylmaleimide resulted in a concentration-dependent reduction of the specific binding of [3H]GBR 12783 (1-[2-(diphenylmethoxy)ethyl]4-(3-phenyl-2-[1-3H]propenyl)-piperaz ine) which was significantly more marked than that of the specific binding of [3H]cocaine, the nonspecific binding of [3H]cocaine being measured with either cocaine or dopamine. Addition of substrates or pure uptake inhibitors to the treatment medium afforded protection against the N-ethylmaleimide-induced reduction in both bindings. In particular, cocaine offered protection for [3H]GBR 12783 binding and vice versa. All results are consistent with a model in which pure uptake blockers and substrates recognize nonidentical but overlapping binding domains on the neuronal carrier of dopamine.
Saadouni
S
S
EP 076 du C.N.R.S., U.F.R. de Médecine & Pharmacie de Rouen, Saint Etienne du Rouvray, France.
Refahi-Lyamani
F
F
Costentin
J
J
Bonnet
J J
JJ
D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D003042:Cocaine / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D010879:Piperazines / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D010879:Piperazines; C039737:1-(2-(diphenylmethoxy)ethyl)-4-(3-phenyl-2-propenyl)piperazine; D003042:Cocaine; D005033:Ethylmaleimide; D004298:Dopamine