CHARACTERIZATION OF (5Z)-7-[3-ENDO-[(4-IODOPHENYLSULFONYL) AMINO]-BICYCLO[2.2.1]HEP-2-EXO-YL]HEPTENOIC ACID (IS-145) AS AN ANTAGONIST FOR THE STUDY OF THROMBOXANE-A2 RECEPTOR

(5Z)-7-[3-endo-[(4-iodophenylsulfonyl) amino]bicyclo[2.2.1]-hep-2-exo- yl] heptenoic acid (IS-145) was characterized on its suitability for t he study of thromboxane A2 (TXA2) receptor. Both the I-125 and I-127 a nalogs are very potent TXA2 antagonist. The I-127 analog interacted wi th the receptor specifically as shown by the displacement of [H-3]-SQ2 9548 from its binding sites on human platelet membranes in a dose depe ndent manner. It also elicited specific biological responses by inhibi ting I-BOP induced platelet aggregation. However, they failed to inhib it those induced by platelet activating factor. Moreover, it interfere d with the TXA2 receptor activated signal transduction system by inhib iting I-BOP induced increase in GTP-gamma-[S-35] binding and GTPase ac tivity. These data indicated that IS-145 was indeed a specific antagon ist. The I-125 analog was used as a radioactive ligand to characterize TXA2 receptor in human platelet membranes. The binding was found to b e saturable, reversible and specific with a K(D) of 5.8 nM and a Bmax of 1.9 pmol/mg protein.