Characterization of serotonin binding sites on human platelets.

A high affinity, saturable 3H-spiroperidol binding site was identified for the first time on the intact human platelet, with drug affinities comparable to the serotonin-2 (S-2) receptor in human frontal cortex. The site was characterized by a KD of 2.7 +/- 0.3nM and a Bmax of 1.4 +/- 0.2 pmoles/10(8) platelets. A 3H-serotonin binding site was also found, with a KD of 42 +/- 8 nM, which appeared to represent the serotonin uptake site. No 3H-serotonin binding site with features of the serotonin-1 (S-1) receptor in brain was found on the platelet. Assay of 3H-spiroperidol binding to platelets may serve as an easily applied model for studying S-2 receptor function in man, and its relationship to age, hormonal, drug, and disease effects.