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

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 Vmax 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 Kd values for 3H-imipramine binding but the Km 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 Bmax and Vmax values or the Kd and Km values. These results suggest that although the 3H-imipramine binding site and the mechanism for serotonin uptake are associated, they are not identical.