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Cationic and Anionic Requirements for the Binding of 2β-Carbomethoxy-3β-(4-Fluorophenyl)[3H]tropane to the Dopamine Uptake Carrier


Address correspondence and reprint requests to Dr. M. E. A. Reith at Department of Basic Sciences, University of Illinois College of Medicine, Box 1649, Peoria, IL 61656, U.S.A.


Abstract: The present study reports the ion dependency of 2β-carbomethoxy-3β-(4-fluorophenyl)[3H]tropane ([3H]- CFT) binding to the dopamine transporter in the rat striaturn. 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 l-, but is unaffected or only slightly affected by F-, Cl-, Br-, NO3-, or SO42-, Concentrations of Na+ of >50 mM become inhibitory except in the presence of l-, 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 NaCIversus 10 mM plus 40 mM NaCI; or 1 mM plus 129 mM Nal versus 10 mM plus 120 mM Nal). No differences were observed in the density of CFT binding sites between any of the conditions examined.