Benzodiazepine receptors on human blood platelets.

Abstract Binding studies conducted on membrane preparation from human platelets using ( 3 H) Ro5-4864 and ( 3 H) diazepam showed specific and saturable binding. Scatchard analysis revealed a single class of binding sites with K D = 10.8 ± 0.9 and Bmax = 775 ± 105 fmol/mg protein for ( 3 H) Ro5-4864 and K D = 10.5 ± 1.1 nM and Bmax = 133 ± 19 fmol/mg for ( 3 H) diazepam. We were unable to detect any GABA binding site on crude membrane preparation, nor did GABA enhance the binding of ( 3 H) Ro5-4864 or ( 3 H) diazepam. This suggests that benzodiazepine receptors are uncoupled to GABA system on human platelets. Ro15-1788, a specific antagonist for “central type” benzodiazepine (BDZ) binding sites was inactive in displacing ( 3 H) Ro5-4864 from membrane receptors, while PK 11195 (a specific ligand for the “peripheral type” receptor) was the most potent of the drugs tested in inhibiting ( 3 H) Ro5-4864 binding. These results indicate that human blood platelets bear “peripheral-type” BDZ receptor. Moreover, we could not detect any ( 3 H) propyl β carboline specific binding on platelet membranes. Results on benzodiazepine receptors on human circulating lymphocytes are also reported and similarity in pharmacological properties with platelet benzodiazepine receptors is suggested.