title: Characterization of binding of a specific antagonist, [3H]-SQ 29,548, to soluble thromboxane A2/prostaglandin H2 (TP) receptors in human platelet membranes.
abstract: Binding of [3H]-SQ 29,548 was characterized to soluble thromboxane A2/prostaglandin H2 (TP) receptors from human platelet membranes as a means of examining ligand-receptor interactions outside the lipophilic environment of the cell membrane. Kinetic determination revealed a rate of ligand-receptor association of 1.4 x 10(7) +/- 0.2 M-1 x min-1 and a rate of dissociation of 0.5 +/- 0.07 min-1. The resultant equilibrium affinity constant was 36.3 +/- 5.8 nM. Saturation binding analysis revealed a single class of [3H]-SQ 29,548 binding sites with an affinity constant of 39.7 +/- 4.3 nM and a B(max) of 1735.7 +/- 69.1 fmol/mg protein. Specific [3H]-SQ 29,548 binding was inhibited by specific TP receptor antagonists and agonists in a rank order of potency similar to that seen in platelet membranes: SQ 33,961 much greater than SQ 29,548 greater than BM 13,505 greater than or equal to U 46619 greater than BM 13,177. PGD2, PGE2 and PGI2 did not appreciably inhibit the specific binding of [3H]-SQ 29,548. These data indicate that [3H]-SQ 29,548 binding to soluble human platelet TP receptors was specific, saturable, and reversible.
authors.affiliation: Department of Cardiovascular Biochemistry, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, N.J. 08543.
authors.forename: H
authors.initials: H
authors.lastname: Monshizadegan
authors.forename: A
authors.initials: A
authors.lastname: Hedberg
authors.forename: M L
authors.initials: ML
authors.lastname: Webb
mesh_terms: D001792:Blood Platelets / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002462:Cell Membrane / Q000378:metabolism; D005231:Fatty Acids, Unsaturated; D006801:Humans; D006834:Hydrazines / Q000378:metabolism* / Q000494:pharmacology; D011448:Prostaglandin Antagonists / Q000494:pharmacology; D011463:Prostaglandins H / Q000097:blood*; D011982:Receptors, Prostaglandin / Q000187:drug effects / Q000378:metabolism*; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D012995:Solubility; D013928:Thromboxane A2 / Q000037:antagonists & inhibitors* / Q000097:blood / Q000494:pharmacology
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines; D011448:Prostaglandin Antagonists; D011463:Prostaglandins H; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2; C045749:SQ 29548