Radiolabeling of dopamine uptake sites in mouse striatum: comparison of binding sites for cocaine,mazindol, and GBR 12935 |
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Authors: | Maarten E A Reith Gabor Selmeci |
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Institution: | (1) Division of Neurochemistry, N. S. Kline Institute for Psychiatric Research, Oak and Plaza Sts, 10962 Orangeburg, NY, USA;(2) Department of Basic Sciences, University of Illinois School of Medicine at Peoria, P.O. Box 1649, 61656 Peoria, IL, USA |
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Abstract: | Summary This study addressed the possibility of a unique binding interaction between cocaine and the dopamine transporter as compared with other blockers of dopamine uptake. Cocaine binding sites in a fresh P2 fraction of mouse striatum were labeled with 3H]CFT, a phenyltropane analog of cocaine also known as WIN 35,428, and compared with sites labeled with 3H]mazindol or 3H]GBR 12935. Under the conditions used, homogeneous binding was observed that was inhibited monophasically by cocaine, CFT, and mazindol; the same potencies were observed with the three radioligands. Saturation analysis in the presence and in the absence of unlabeled inhibitor (CFT, mazindol, cocaine) indicated a change in the Kd but not the Bmax, consonant with a competitive mechanism. Tris-HCl reduced the affinity of each radioligand and unlabeled inhibitor without changing the Bmax. N-Ethylmaleimide reduced the binding of all radioligands equally and cocaine offered protection. The dissociation rate of 3H]CFT and 3H]mazindol binding was not affected by the presence of mazindol and CFT, respectively. The Bmax of 3H]CFT and 3H]mazindol binding was the same; the relatively higher value for 3H]GBR 12935 binding in analyses involving varying tritiated GBR 12935 only, was due primarily to an underestimation of the specific activity of 3H]GBR 12935. All results are in agreement with a one-site model in which cocaine, CFT, mazindol, and GBR 12935 share a common binding site in mouse striatum. |
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Keywords: | Cocaine binding Mazindol binding GBR 12935 binding N-ethylmaleimide Mouse striatum |
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