Imipramine binding in subpopulations of normal human blood platelets

Imipramine binding was studied in platelet membranes isolated with different proportions of heavy (young) and light (old) platelets. The Bmax, a measure of the number of binding sites, was greater in the heavier platelets than in the light platelets. However, the dissociation constant Kd (a reflection of the affinity of imipramine binding) was greater in the lighter platelets compared to the heavy platelets. These results indicate that differences in Kd and Bmax in particular membrane preparation, could be due to the differences in the relative proportion of heavy and light platelets.