Proteinase-activated receptor-2 activating peptides: distinct canine coronary artery receptor systems

In canine coronary artery preparations, the proteinase-activated receptor-2 ([PAR.sub.2]) activating peptides ([PAR.sub.2]-APs) SLIGRL-[NH.sub.2] and 2-furoyl-LIGRLO-[NH.sub.2] caused both an endothelium-dependent relaxation and an endothelium-independent contraction. Relaxation was caused at peptide concentrations 10-fold lower than those causing a contractile response. Although trans-cinnamoyl-LIGRLO-[NH.sub.2], like other [PAR.sub.2]-APs, caused relaxation, it was inactive as a contractile agonist and instead antagonized the contractile response to SLIGRL-[NH.sup.2]. RT-PCR-based sequencing of canine [PAR.sup.2] revealed a cleavage/activation (indicated by underlines) sequence (SKGR/SLIGKTDSSLQITGKG) that is very similar to the human [PAR.sup.2] sequence (R/SLIGKV). As a synthetic peptide, the canine PAR-AP (SLIGKT-[NH.sub.2]) was a much less potent agonist than either SLIGRL-[NH.sub.2] or 2-furoyl-LIGRLO-[NH.sub.2], either in the coronary contractile assay or in a Madin-Darby canine kidney (MDCK) cell [PAR.sub.2] calcium signaling assay. In the MDCK signaling assay, the order of potencies was as follows: 2-furoyl-LIGRLO-[NH.sub.2] [much greater than] SLIGRL-[NH.sub.2] = trans-cinnamoyl-LIGRLO-[NH.sub.2] [much greater than] SLIGKT-[NH.sub.2], as expected for [PAR.sub.2] responses. In the coronary contractile assay, however, the order of potencies was very different: SLIGRL-[NH.sub.2] [much greater than] 2-furoyI-LIGRLO-[NH.sub.2] [much greater than] SLIGKT-[NH.sub.2], trans-cinnamoyl-LIGRLO-[NH.sub.2] = antagonist. Because of 1) the distinct agonist (relaxant) and antagonist (contractile) activity of trans-cinnamoyl-LIGRLO-[NH.sub.2] in the canine coronary contractile assays, 2) the different concentration ranges over which the peptides caused either relaxation or contraction in the same coronary preparation, and 3) the markedly distinct structure-activity profiles for the PAR-APs in the coronary contractile assay, compared with those for [PAR.sub.2]-mediated MDCK cell calcium signaling, we suggest that the canine coronary tissue possesses a receptor system for the PAR-APs that is distinct from [PAR.sub.2] itself. protease; vascular G protein-coupled receptor