TP receptors (Thromboxane A2 receptors) are widely distributed among different organ systems and have been localized on both cell membranes and intracellular structures. TP receptors belong to the prostanoid G protein-coupled receptor family. Activation of TP receptors induces platelet aggregation, vascular and respiratory smooth muscle constriction, and enhances mitogenic responses of vascular smooth muscle cells that are stimulated by growth factors. The human TP receptor is encoded by a single gene that is alternatively spliced at the carboxyl terminus, resulting in two isoforms, TP (343 residues) and TP (407 residues). Both isoforms couple to Gq pathway, but couple oppositely to adenylate cyclase. The cDNA encoding human TP has been stably expressed in these TP receptor-expressing cells.