5-HYDROXYTRYPTAMINE (5-HT)-INDUCED SHAPE CHANGE IN HUMAN PLATELETS DETERMINED BY COMPUTERIZED DATA ACQUISITION - CORRELATION WITH [I-125] IODOLSD BINDING AT 5-HT2 RECEPTORS

The 5-HT-induced shape change and subsequent aggregation of platelets provides a functional assay for 5-HT2 receptors. In the present study we describe a method to increase aggregometer sensitivity by digital conversion of the voltage produced by changes in light transmittance through a platelet suspension, thereby allowing accurate analyses of the primary shape-change response. The pharmacology of 5-HT-induced shape change was then compared with that of [I-125]-iodoLSD binding in human platelets. 5-HT caused a dose-dependent change in platelet shape (maximum response 5 x 10(-6) M, EC50 10(-6) M). Furthermore, there was a significant correlation across a selection of drugs between IC50 values for inhibition of 5-HT-induced shape change and for inhibition of platelet binding of the 5-HT2 receptor ligand [I-125]-iodoLSD. These results support the hypothesis that 5-HT-induced shape change and [I-125]-iodoLSD binding in human platelets are mediated through the same receptor, and validate the methods of data acquisition described.