HUMAN PLATELET 5-HT2 RECEPTOR-BINDING SITES REEVALUATED - A CRITICISMOF RECURRENT TECHNIQUES

The human platelet 5-HT2 receptor may resemble a peripheral model of c entral 5-HT2 binding sites and has been linked to changes in 5-HT2 rec eptor function in depression. Therefore, evaluation of the human plate let 5-HT2 binding characteristics is important. Comparing [H-3]ketanse rin and [H-3]LSD as ligands clearly indicated [H-3]LSD as ligand of ch oice for binding studies dealing with the human platelet 5-HT2 recepto r. [H-3]LSD binding was specific, saturable, and depended upon incubat ion time, protein concentration and previous handling of tissue, i.e., use of fresh or frozen tissue. In contrast, studies with [H-3]ketanse rin were unsatisfactory. Although mean receptor densities and affiniti es have been relatively constant between individuals and over time in healthy subjects with [H-3]LSD, examination of the individual data sho wed considerable variations within single subjects. Thus, K(D) ranged between 0.50 and 0.68 nM, and B(max) was in the range of 64.9 to 97.1 fmol/mg protein in healthy individual subjects. Therefore, we recommen d [H-3]LSD as ligand of choice to study platelet 5-HT2 receptor bindin g in humans. Furthermore, repeated measurement of individual data over time should be interpreted cautiously, especially when data from depr essed patients are under examination.