Vol. 303, Issue 3, 985-992, December 2002

Proteinase-Activated Receptor-2 (PAR2): Vascular Effects of a PAR2-Derived Activating Peptide via a Receptor Different than PAR2

John J. McGuire, Jiazhen Dai, Patricia Andrade-Gordon¹, Chris R. Triggle and Morley D. Hollenberg

Smooth Muscle Research Group, Department of Pharmacology and Therapeutics, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada

We studied the actions of the proteinase-activated receptor-2-activating peptide (PAR2-AP) trans-cinnamoyl-LIGRLO-amide (tc-LI) in femoral (FA), renal, and small mesenteric (MA) arterial vessels from C57BL/6 [PAR2 (+/+)] and PAR2 (/) mice. The actions of tc-LI were compared with those of the parent PAR2-AP Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-amide; SLI-NH₂). Either SLI-NH₂ or tc-LI (0.1-10 µM) induced relaxation of either 9,11-dideoxy-9,11-methanoepoxy-prosta-5Z,13E-dien-1-oic acid (U46619)- or cirazoline-precontracted FA from PAR2 (+/+) in endothelium-intact preparations but did not relax vessels from PAR2 (/) mice. This FA relaxation by SLI-NH₂ and by tc-LI was inhibited by 1) pretreatment with a combination of L-N^G-nitroarginine methyl ester (L-NAME) and 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), 2) precontraction with 30 mM KCl, or 3) removal of the endothelium. In contrast, tc-LI caused an L-NAME/ODQ/indomethacin-resistant relaxation of MA from PAR2 (+/+) mice. In contrast with SLI-NH₂, tc-LI (>30 µM) contracted arteries from both PAR2 (/) and PAR2 (+/+) mice. Pretreatment of tissues with a combination of cyclopiazonic acid plus caffeine reduced significantly tc-LI-induced contractions, whereas nifedipine, CdCl₂, and Ca²⁺-free conditions did not. Inhibitors of vascular muscarinic, ₁-adrenergic, neurokinin, thromboxane A₂, histamine, angiotensin II, or endothelin-1 receptors failed to inhibit contractions by 50 µM tc-LI. At resting tension, SLI-NH₂ (>10 µM) contracted all arteries in an endothelium-independent manner but only from PAR2 (+/+) mice. We conclude that the endothelium-dependent vasodilation initiated by SLI-NH₂ and tc-LI, but not the endothelium-independent contraction initiated by tc-LI, are due to the activation of PAR2. Indeed, the data from PAR2 (/) mice indicate that tc-LI, in addition to activating PAR2, is an agonist of vascular smooth muscle contraction via a receptor different than PAR2.