Purity >98%. The lipid mediator thromboxane (TX)A2 plays a key role in platelet aggregation and vascular and bronchial smooth muscle constriction. The actions of TXA2 are mediated by its specific G protein-coupled receptor, referred to as the TXA2 receptor or TP. Two isoforms, TPAlpha and TPBeta, are produced from a single gene, differ in their carboxyl termini, and form homo- and hetero-oligomers. While both isoforms signal through similar pathways, they differ in the modulation by certain agonists. L-655,240 is a potent antagonist of the TP receptor in vitro (IC50 = 7 nM). It also is effective at blocking TP-mediated bronchoconstriction in vivo and platelet aggregation ex vivo . Whether the two TP isoforms differ in their sensitivity to L-655,240 is not known.