Cationic and anionic requirements for the binding of 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)[3H]tropane to the dopamine uptake carrier.
The present study reports the ion dependency of 2 beta-carbomethoxy-3 beta-(4-fluorophenyl)[3H]tropane ([3H]CFT) binding to the dopamine transporter in the rat striatum. The results indicate that [3H]CFT binding to synaptosomal P2 membranes requires low concentrations of Na+ (peak binding between 20 and 50 mM Na+), is stimulated by phosphate anion or I-, but is unaffected or only slightly affected by F-, Cl-, Br-, NO3-, or SO(4)2-. Concentrations of Na+ of > 50 mM become inhibitory except in the presence of I-, which shifts peak binding levels toward higher Na+ concentrations and also elevates the peak binding level. K+ strongly decreased [3H]CFT binding with a shallow inhibition curve, and Na+ could not overcome this effect. Saturation analysis of [3H]CFT binding revealed a single binding site changing its affinity for CFT depending on the concentration of sodium phosphate buffer (6, 10, 30, 50, 130, or 200 mM; 1 mM plus 49 mM NaCl versus 10 mM plus 40 mM NaCl; or 1 mM plus 129 mM NaI versus 10 mM plus 120 mM NaI). No differences were observed in the density of CFT binding sites between any of the conditions examined.
Reith
M E
ME
Department of Basic Sciences, University of Illinois College of Medicine, Peoria 61656.
Coffey
L L
LL
D000818:Animals; D000838:Anions / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism*; D002412:Cations / Q000494:pharmacology*; D003042:Cocaine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism; D003342:Corpus Striatum / Q000378:metabolism; D050483:Dopamine Plasma Membrane Transport Proteins; D005260:Female; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010710:Phosphates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D014316:Tritium
D000838:Anions; D002352:Carrier Proteins; D002412:Cations; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D010710:Phosphates; D014316:Tritium; C021279:(1R-(exo,exo))-3-(4-fluorophenyl)-8-methyl-8- azabicyclo(3.2.1)octane-2-carboxylic acid, methyl ester; D012964:Sodium; D003042:Cocaine; D011188:Potassium