Comparison of characteristics of dopamine uptake and mazindol binding in mouse striatum

Summary

Biochemical and pharmacological studies suggest that the binding of [³H]mazindol is functionally related to the dopamine uptake carrier complex in rodent striatum. In order to study further the relationship between the substrate recognition site for dopamine uptake and the high-affinity binding site for mazindol the uptake of [³H]dopamine and the binding of [³H]mazindol was studied in BALB/cBy mouse striatum in various buffers (Tris, HEPES, bicarbonate-phosphate). Kinetic analysis showed that theK _d, of the binding of [³H]mazindol and theK _m of the uptake of [³Mdopamine was changed by different sodium concentrations and/or by the presence of Tris, while theB _max, and theV _max remained essentially the same. However, the shape of the Na⁺ dependency curves was not the same for mazindol binding and dopamine uptake in the various buffers. The inhibitory effect of other cations such as K⁺ and Tris was also different on binding and uptake under similar experimental circumstances. Dopamine did not slow down the dissociation of mazindol from its site and this effect was not sodium-sensitive. These complexities can be accomodated by a model that involves overlapping sites for mazindol and dopamine on the dopamine uptake carrier complex, and translocation -reorientation steps.