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.
Department of Basic Sciences, University of Illinois College of Medicine, Peoria 61656.
M E
ME
Reith
L L
LL
Coffey
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