Characterisation of [3H]lysergic acid diethylamide binding to a 5-hydroxytryptamine receptor on human platelet membranes.

Specific binding of [3H]lysergic acid diethylamide (LSD) to human platelet membranes, as defined by 300 nM spiperone, was saturable over the concentration range of 0.25-2.5 nM [3H]LSD. At 0.5 nM [3H]LSD the half-time for association at 37 degrees C was 56 min, half-time for dissociation was 173 min, and the kinetically derived affinity was 0.24 nM. In 19 control subjects equilibrium binding studies gave an affinity of 0.53 +/- 0.02 nM (mean +/- S.E.M.) and capacity of 57.1 +/- 5.6 fmol/mg protein (mean +/- S.E.M.). The inhibition profile was consistent with that of a 5-hydroxytryptamine (5-HT) receptor. There was a significant correlation between the inhibition of [3H]LSD binding and the inhibition of 5-HT-induced shape change, but not inhibition of active platelet uptake of 5-HT. There was also a significant correlation between the inhibition of [3H]LSD binding to human platelet membranes and human frontal cortex. Platelet [3H]LSD binding may therefore be a useful model for study of peripheral and central 5-HT receptors in man.