3H-Imipramine binding and serotonin uptake in platelets from untreated depressed patients and control volunteers

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Abstract
Human platelets possess specific high-affinity binding sites for 3H-imipramine which have similar characteristics to the sites previously described in human and animal brain. In a group of untreated depressed patients, the Bmax of 3H-imipramine binding and the V max of serotonin uptake in their platelets were found to be significantly lower than in a group of control volunteers. There was no significant difference in the K d values for 3H-imipramine binding but the K m values of 3H-serotonin uptake were decreased in the depressed patients. When the measurements of 3H-imipramine binding and 3H-serotonin uptake were compared in the same individual, however, there was no correlation between the individual B max and V max values or the K d and K m values. These results suggest that although the 3H-imipramine binding site and the mechanism for serotonin uptake are associated, they are not identical.