title: [3H]S-145 and [125I]I-S-145-OH: new radioligands for platelet thromboxane A2 receptor with low nonspecific binding and high binding affinity for various receptor preparations.
abstract: Two new radioligands for the TXA2 receptor, [3H]S-145 (5Z-7-(3-endo-[( ring-4-3H]phenyl)sulphonylamino- [2.2.1.]bicyclohept-2-exo-yl) heptenoic acid) and [125I]I-S-145-OH (5Z-7-(3-endo[( 125I] 3-iodo-4-hydroxyphenylsulphonyl)amino- [2.2.1.] bicyclohept-2- yl)heptenoic acid) were synthesized and their binding to washed human platelets, platelet membrane and solubilized TXA2 receptor was examined. Both [3H]S-145 and [125I]I-S-145-OH bound to the above preparations in a saturable and reversible manner. In contrast to the conventional TXA2 receptor ligands, such as [3H]U-46619 and [125I]PTA-OH, nonspecific binding of these radioligands constituted less than 10% of the total binding under the standard assay conditions. Scatchard analysis revealed a single class of binding sites for all three preparations; the Kd values of the [3H]S-145 binding were 3.64, 3.14 and 8.22 nM for washed platelets, platelet membrane and the solubilized receptor, respectively, and those of [125I]I-S-145-OH binding were 5.72 and 4.09 nM for washed platelets and the solubilized receptor, respectively. Thus, [3H]S-145 and [125I]I-S-145-OH are the ligands with low nonspecific binding and the highest affinities for the TXA2 receptor, which are independent of membrane preparation and receptor solubilization. In addition, the alpha-carboxyl group of S-145 could be modified without change in the binding affinity.
authors.affiliation: Department of Pharmacology, Kyoto University Faculty of Medicine, Japan.
authors.forename: F
authors.initials: F
authors.lastname: Ushikubi
authors.forename: M
authors.initials: M
authors.lastname: Nakajima
authors.forename: M
authors.initials: M
authors.lastname: Yamamoto
authors.forename: K
authors.initials: K
authors.lastname: Ohtsu
authors.forename: Y
authors.initials: Y
authors.lastname: Kimura
authors.forename: M
authors.initials: M
authors.lastname: Okuma
authors.forename: H
authors.initials: H
authors.lastname: Uchino
authors.forename: M
authors.initials: M
authors.lastname: Fujiwara
authors.forename: S
authors.initials: S
authors.lastname: Narumiya
mesh_terms: D001386:Azides; D001792:Blood Platelets / Q000378:metabolism*; D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis; D001952:Bridged-Ring Compounds; D002462:Cell Membrane / Q000378:metabolism; D005229:Fatty Acids, Monounsaturated / Q000138:chemical synthesis; D006801:Humans; D007457:Iodine Radioisotopes; D011869:Radioligand Assay; D011982:Receptors, Prostaglandin / Q000037:antagonists & inhibitors / Q000097:blood*; D017482:Receptors, Thromboxane; D012459:Salicylates; D012995:Solubility; D014316:Tritium
chemical_list: D001386:Azides; D001643:Bridged Bicyclo Compounds; D001952:Bridged-Ring Compounds; D005229:Fatty Acids, Monounsaturated; D007457:Iodine Radioisotopes; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D012459:Salicylates; D014316:Tritium; C056566:S 145; C063874:7-(3-iodo-4-hydroxyphenylsulfonylamino(2.2.1)-bicyclohept-2-yl)heptenoic acid; C063873:4-azidosalicylic acid