Searching for the physiological role and therapeutic potential of vascular proteinase-activated receptor-2 (PAR2)

Hyperpolarization of murine small caliber mesenteric arteries by activation of endothelial proteinase-activated receptor 2

Activation of endothelial proteinase-activated receptor 2 (PAR-2) relaxes vascular smooth muscle (VSM) and causes hypotension by nitric oxide (NO)-prostanoid-dependent and -independent mechanisms. We investigated whether endothelium-dependent hyperpolarization of VSM was the mechanism whereby resistance caliber arteries vasodilated independently of NO. VSM membrane potentials and isometric tension were measured concurrently to correlate the electrophysiological and mechanical changes in murine small caliber mesenteric arteries. In uncontracted arteries, the PAR-2 agonist, SLIGRL-NH2 (0.1 to 10 micromol/L), hyperpolarized the VSM membrane potential only in endothelium-intact arterial preparations. This response was unaltered by treatment of arteries with inhibitors of NO synthases (L-NAME), soluble guanylyl cyclase (ODQ), and cyclooxygenases (indomethacin). L-NAME, ODQ, and indomethacin also failed to inhibit SLIGRL-NH2-induced hyperpolarization and of cirazoline-contracted mesenteric arteries. However, in blood vessels that were depolarized and contracted with 30 mmol/L KCl, the effects of the SLIGRL-NH2 on membrane potential and tension were not observed. SLIGRL-NH2-induced hyperpolarization and relaxation was inhibited completely by the combination of apamin plus charybdotoxin, but only partially inhibited after treatment with the combination of barium plus ouabain, suggesting an important role for SKCa and IKCa channels and a lesser role for Kir channels and Na+/K+ ATPases in the hyperpolarization response. We concluded that activation of endothelial PAR-2 hyperpolarized the vascular smooth muscle (VSM) cells of small caliber arteries, without requiring the activation of NO synthases, cyclooxygenases, or soluble guanylyl cyclase. Indeed, this hyperpolarization may be a primary mechanism for PAR-2-induced hypotension in vivo.

2-Furoyl-LIGRLO-amide: A Potent and Selective Proteinase-Activated Receptor 2 Agonist

A peptide corresponding to a proteinase-activated receptor 2 (PAR(2))-activating peptide with an N-terminal furoyl group modification, 2-furoyl-LIGRLO-NH(2), was assessed for PAR(2)-dependent and -independent biological activities. 2-Furoyl-LIGRLO-NH(2) was equally effective to and 10 to 25 times more potent than SLIGRLNH(2) for increasing intracellular calcium in cultured human and rat PAR(2)-expressing cells, respectively. In bioassays of tissue PAR(2) activity, measured as arterial vasodilation and hyperpolarization, 2-furoyl-LIGRLO-NH(2) was 10 to 300 times more potent than SLIGRL-NH(2). Unlike trans-cinnamoyl-LIGRLO-NH(2), 2-furoyl-LI-GRLO-NH(2) did not cause a prominent non-PAR(2)-mediated contraction of murine femoral arteries. In conclusion, 2-furoyl-LI-GRLO-NH(2) represents the most potent and selective activator of PAR(2) in biological systems described to date.