title: Characterization of U46619 binding in unactivated, intact human platelets and determination of binding site affinities of four TXA2/PGH2 receptor antagonists (13-APA, BM 13.177, ONO 3708 and SQ 29,548).
abstract: The binding of U46619 and the inhibition of this binding by four TXA2/PGH2 receptor antagonists (13-APA, BM 13.177, ONO 3708 and SQ 29,548) were studied in unactivated, intact human platelets. Washed platelets were equilibrated with [3H]-U46619 (5 nM) and the time course of binding determined. The receptor-specific binding reached equilibrium within 2-4 minutes, and could be displaced by addition of excess unlabelled ligand. Saturation of this binding was achieved at 750 nM. Scatchard transformation of the saturation binding curve yielded a single class of binding site with a Kd of 108 nM and Bmax of 360 fmole/10(8) platelets. When [3H]-U46619 (4 nM) was incubated with platelets in the presence of increasing concentrations of the antagonists, binding of U46619 was inhibited in a dose dependent manner. The potency series for inhibition of U46619 binding was: SQ 29,548 (IC50 = 7.9 nM) greater than ONO 3708 (IC50 = 38 nM) greater than BM 13.177 (IC50 = 0.91 microM) greater than 13-APA (IC50 = 6.2 microM). These findings are consistent with the notion that these compounds all act as competitive antagonists at the level of the platelet TXA2/PGH2 receptor.
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010974:Platelet Aggregation; D011448:Prostaglandin Antagonists / Q000494:pharmacology*; D011449:Prostaglandin Endoperoxides / Q000097:blood*; D011450:Prostaglandin Endoperoxides, Synthetic / Q000097:blood*; D011463:Prostaglandins H / Q000097:blood*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013931:Thromboxanes / Q000097:blood*
chemical_list: D011448:Prostaglandin Antagonists; D011449:Prostaglandin Endoperoxides; D011450:Prostaglandin Endoperoxides, Synthetic; D011463:Prostaglandins H; D011956:Receptors, Cell Surface; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013931:Thromboxanes; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid