Demonstration of S2-receptor binding sites on cat blood platelets using [3H]ketanserin

[3H]Ketanserin showed substantial binding to cat platelet membranes; 40% of this was specific binding, characterized by a plateau in serotonin antagonist inhibition curves, and another 40% was non-specific binding to structural recognition sites displaceable by unlabelled ketanserin. Specific [3H]ketanserin binding to platelets shows the features of serotonin S2-receptor binding sites previously identified in rat pre-frontal cortex and in striatum. In platelets, KD = 1.02 nM and Bmax = 86 fmol/10(9) platelets; the Ki values of 21 compounds were similar in the three different tissues.