Relationship between 3H-imipramine binding, 14C-serotonin uptake, and the surface area of blood platelets

1. The relationship between 14C-serotonin uptake, 3H-imipramine binding and surface area was studied in blood platelets. 2. Platelet rich plasma from 5 normal subjects was divided into 5 size subfractions by differential centrifugation and the total surface areas computed from platelet size profiles. 3. Linear relationships were found between both uptake and binding as a function of surface area regardless of platelet size. 4. The results suggest that platelet heterogeneity may contribute to the variability of uptake measurements which are commonly expressed on a per platelet basis. In contrast, the importance of heterogeneity to binding measurements, which are expressed per unit protein, may have been previously overestimated.