THE COCAINE ANALOG WIN 35,428 BINDS TO 2 SITES IN FRESH RAT CAUDATE-PUTAMEN - SIGNIFICANCE OF ASSAY PROCEDURES

Binding of the potent cocaine analog [H-3]WIN 35,428 (2beta-carbomethoxy-3beta-(4-fluoro-phenyl)-tropane) was examined in membrane homogenates prepared from fresh rat caudate-putamen. The number of rinses of the membranes following incubation with the ligand was varied. After one wash, only a single binding site was evident. With an increasing number of washes, however, two binding sites were observed. Additional rinses, up to a total of four, led to a decrease in the number of low affinity binding sites, with no change in the number of high affinity sites. These results suggest that the methodology used in these binding assays may be important for interpretation of the results.