Detection of functional receptors for the proteinase-activated-receptor-2-activating polypeptide, SLIGRL-NH2, in rat vascular and gastric smooth muscle

Abstract

We have studied the actions of the proteinase-activated-receptor-2 (PAR₂)-activating polypeptide, SLIGRL-NH₂(SLI-NH₂), in rat aorta and in gastric longitudinal muscle preparations. In the phenylephrine-precontracted aorta preparation, SLI-NH₂caused an endothelium-dependent relaxation that mimicked the action of low concentrations (0.5 U/mL) of trypsin and that was blocked by the nitric oxide synthase inhibitor N^ω-nitro-L-arginine methyl ester. In endothelium-free aorta ring preparations, SLI-NH₂caused neither a relaxation nor a contraction. In the gastric longitudinal muscle preparation, SLI-NH₂caused a transient contraction that mimicked the action of trypsin (0.5 U/mL) and that was sensitive to inhibitors of cyclooxygenase (indomethacin) and tyrosine kinase (genistein). Further, using a reverse-transcriptase – polymerase chain reaction (RT–PCR) approach we detected, in both assay tissues, mRNA for the rat PAR₂receptor, and we ascertained, using a cloned receptor cDNA obtained from a rat intestinal cDNA library, that the putative N-terminal activating peptide sequence of the rat PAR₂receptor (SLIGRL) is identical with the one previously cloned from murine tissue. We concluded that, like the thrombin receptor, the PAR₂receptor may play a pathophysiologic role in the regulation of vascular and gastric smooth muscle contractility.Key words: thrombin, proteinase-activated receptor 2, protease, smooth muscle.