Submitted on April 30, 2007
Accepted on August 28, 2007
Proteinase-activated receptor-2 activating peptides: Distinct canine coronary artery receptor systems
Mahmoud Saifeddine1, Michelle L Seymour2, Yu-Pei Xiao3, Steven John Compton4, Steeve Houle5, Rithwik Ramachandran1, Wallace K. MacNaughton2, Serge Simonet6, Christine Vayssettes-Courchay6, Tony J Verbeuren6, and Morley D Hollenberg5*
1 Pharmacology, University of Calgary Faculty of Medicine, Calgary, Canada
2 Physiology, University of Calgary Faculty of Medicine, Calgary, Canada
3 Respiratory Medicine, University of Hull, Hull, United Kingdom
4 Respiratory Medicine, University of Hull, Hull, East Yorkshire, United Kingdom
5 Pharmacology & Therapeutics, and Medicine, University of Calgary, Calgary, Canada
6 Division of Angiology, Institut de Recherches Servier, Suresnes, France
* To whom correspondence should be addressed. E-mail: mhollenb{at}ucalgary.ca.
In canine coronary artery preparations, the proteinase-activated receptor-2 (PAR2) activating peptides (PAR2APs), SLIGRL-NH2 and 2-furoyl-LIGRLO-NH2 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-NH2, like other PAR2APs caused relaxation, it was inactive as a contractile agonist and instead antagonized the contractile response to SLIGRL-NH2. RT-PCR-based sequencing of canine PAR2 revealed a cleavage/activation sequence (SKGR/SLIGKTDSSLQITGKG) that is very similar to the human PAR2 sequence (R/SLIGKV). As a synthetic peptide, the canine PAR-AP (SLIGKT-NH2) was a much less potent agonist than either SLIGRL-NH2 or 2-furoyl-LIGRLO-NH2 both in the coronary contractile assay and in a canine MDCK cell PAR2 calcium signaling assay. In the MDCK signaling assay, the order of potencies was: 2-furoyl-LIGRLO-NH2>>SLIGRL-NH2=trans-cinnamoyl-LIGRLO-NH2>> SLIGKT-NH2, as expected for PAR2 responses, whereas in the coronary contractile assay, the order of potencies was very different: SLIGRL-NH2>>2-furoyl-LIGRLO-NH2>> SLIGKT-NH2; trans-cinnamoyl-LIGRLO-NH2=antagonist. Due to: (1) the distinct agonist (relaxant) and antagonist (contractile) activity of trans-cinnamoyl-LIGRLO-NH2 in the canine coronary bioassay, (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 the PAR2-profile in the canine MDCK cell calcium signaling assay, we suggest that the canine coronary tissue possesses a receptor system for the PAR-APs that is distinct from PAR2 itself.
