[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

Eicosanoids. 1989;2(1):21-7.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Azides
  • Blood Platelets / metabolism*
  • Bridged Bicyclo Compounds* / chemical synthesis
  • Bridged-Ring Compounds*
  • Cell Membrane / metabolism
  • Fatty Acids, Monounsaturated* / chemical synthesis
  • Humans
  • Iodine Radioisotopes
  • Radioligand Assay
  • Receptors, Prostaglandin / antagonists & inhibitors
  • Receptors, Prostaglandin / blood*
  • Receptors, Thromboxane
  • Salicylates
  • Solubility
  • Tritium

Substances

  • Azides
  • Bridged Bicyclo Compounds
  • Bridged-Ring Compounds
  • Fatty Acids, Monounsaturated
  • Iodine Radioisotopes
  • Receptors, Prostaglandin
  • Receptors, Thromboxane
  • Salicylates
  • Tritium
  • S 145
  • 7-(3-iodo-4-hydroxyphenylsulfonylamino(2.2.1)-bicyclohept-2-yl)heptenoic acid
  • 4-azidosalicylic acid