Binding domains for blockers and substrates on the dopamine transporter in rat striatal membranes studied by protection against N-ethylmaleimide-induced reduction of [3H]WIN 35,428 binding.
Binding sites for 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)[3H]tropane ([3H]WIN 35,428) on rat striatal membranes were alkylated with N-ethylmaleimide (NEM), and the protective potency was measured of the blockers cocaine, N[1-(2-benzo[b]thiophenyl) cyclohexyl]piperidine (BTCP), benztropine, WIN 35,428; and nomifensine, and of the substrates dopamine, norepinephrine, S(+)-amphetamine, tyramine, and metaraminol. In general, the protective potency was lower (at least 3 times) than the potency in inhibiting [3H]WIN 35,428 binding with the compounds present under the same experimental conditions used for the NEM-induced alkylation. However, the disparity was substantially greater for all substrates tested (10- to 93-fold) than for the blockers (2- to 6-fold), especially cocaine and BTCP (3-fold). [3H]WIN 35,428 binding was best described by a l-site model under the present conditions. The results are discussed in terms of models involving blocker-induced conformational changes and overlapping nonidentical binding domains for blockers and substrates.
Xu
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Department of Biology, Illinois State University, Normal, USA.
Coffey
L L
LL
Reith
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ME
D000661:Amphetamine / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D003042:Cocaine / Q000031:analogs & derivatives* / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D011487:Protein Conformation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology; D014316:Tritium
D002352:Carrier Proteins; D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D014316:Tritium; C021279:(1R-(exo,exo))-3-(4-fluorophenyl)-8-methyl-8- azabicyclo(3.2.1)octane-2-carboxylic acid, methyl ester; D012964:Sodium; D000661:Amphetamine; D003042:Cocaine; D005033:Ethylmaleimide; D004298:Dopamine