title: A common binding site for primary prostanoids in vascular smooth muscles: a definitive discrimination of the binding for thromboxane A2/prostaglandin H2 receptor agonist from its antagonist.
abstract: Differences in binding characteristics between agonists and antagonists for the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor were examined in rat cultured vascular smooth muscle cells (VSMC). Scatchard analysis indicated the existence of two binding sites for the TXA2/PGH2 agonist, whereas a single class of recognition sites for the receptor antagonists were observed with approximately the same maximum binding capacity (Bmax) as a high-affinity binding site of the agonist. Weak binding inhibition by approx. 100 nM of primary prostanoids (PGE1, PGF2 alpha and PGD2) was detected only with the TXA2/PGH2 agonist, and not with the antagonist. Primary prostanoids as well as TXA2/PGH2 agonists (U46619 and STA2) suppressed the [3H]PGF2 alpha and [3H]PGE1 binding with almost the same potency, whereas TXA2/PGH2 antagonists (S-145, SQ29,548 and ONO3708) did not. The Bmax value of the binding sites was roughly identical in PGF2 alpha, PGE1 and a low-affinity binding site of U46619. These results suggest the existence of two binding sites for TXA2/PGH2 in VSMC, i.e., a high-affinity binding site corresponding to that of the TXA2/PGH2 antagonists and a low-affinity binding site in common with primary prostanoids.
authors.affiliation: Shionogi Research Laboratories, Shionogi & Co. Ltd., Fukushima-ku, Osaka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Hanasaki
authors.forename: H
authors.initials: H
authors.lastname: Arita
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D007700:Kinetics; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011449:Prostaglandin Endoperoxides / Q000378:metabolism*; D011463:Prostaglandins H / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2 / Q000378:metabolism*
chemical_list: D011449:Prostaglandin Endoperoxides; D011463:Prostaglandins H; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2