ABSTRACT
Proteinase-activated receptor-2 (PAR2) is a G protein-coupled receptor activated by serine proteinases like trypsin, which unmasks an N-terminal cryptic tethered-ligand, or by synthetic peptides that mimic the tethered-ligand. In capacitance vessels (aorta, femoral), PAR2 causes an endothelium-dependent, NO-mediated relaxation. It was hypothesized that PAR2 would also release an endothelium-derived hyperpolarizing factor (EDHF) from resistance vessels like mesenteric or renal afferent arterioles. Using SLIGRL-NH2 or trypsin as agonists in either isolated murine mesenteric rings or in perfused rat renal preparations in vitro, the relaxant effects of activating PAR2 were evaluated in the absence or presence of inhibitors of cyclooxygenases, NO synthase and soluble guanylyl cyclase, of elevated extracellular K and of the combination charybdotoxin plus apamin. The effects of PAR2 agonists were compared with the actions of acetylcholine. In contrast with the relaxant effects of SLIGRL-NH2 and acetylcholine in murine aorta or femoral artery, that were both blocked by combined NO synthase/cyclooxygenase/soluble guanylyl cyclase inhibition, in small mesenteric arteries the endothelium-dependent relaxant actions of SLIGRL-NH2 essentially were unaffected by these inhibitors whilst vasodilatation by acetylcholine was blocked. In the rat renal preparations, trypsin and SLIGRL-NH2 caused an initial transient vasodilatation. The transient vasodilatation was resistant to NO synthase/cyclooxygenase/soluble guanylyl cyclase inhibition, but was absent in the presence of 25mM K, pointing to an endothelium-dependent hyperpolarizing activity. However, PAR2-mediated dilatation was not blocked by charybdotoxin plus apamin as was the response to acetylcholine. In conclusion, PAR2 causes an endothelium-dependent hyperpolarization differing from that mediated by acetylcholine. In addition, different G proteincoupled receptors acting in the same tissue can produce distinct endothelium-dependent hyperpolarizing factors.
