Evidence for the presence of a proteinase-activated receptor distinct from the thrombin receptor in vascular endothelial cells.
The thrombin receptor was the first cloned G protein-coupled receptor reported to be activated by proteolytic cleavage of its extracellular amino terminus. A second proteinase-activated receptor (PAR-2) was cloned recently and expressed in Xenopus laevis oocytes. PAR-2 was activated by trypsin and by a peptide (SLIGRL) derived from the new amino terminus. Since PAR-2 mRNA was detected in highly vascularized organs, we compared the physiological functions of the thrombin receptor and PAR-2 in vascular endothelium. Thrombin and trypsin both elicited endothelium-dependent relaxations in prostaglandin F2alpha (PGF2alpha)-contracted strips of porcine coronary artery. Whereas high doses of both thrombin or trypsin (10 U/mL) caused homologous desensitization, trypsin caused further relaxation of thrombin-desensitized tissues. Thrombin and PAR-2-derived peptides (SFLLRN and SLIGRL) both induced endothelium-dependent relaxations in PGF2alpha-contracted porcine coronary arteries. SFLLRN or SLIGRL (30 micronmol/L) also showed homologous desensitization but not cross desensitization. In the presence of the NO synthase inhibitor NG-monomethyl-L-arginine (1 mmol/L), both SFLLRN- and SLIGRL-induced relaxations were partially inhibited. SFLLRN elicited weak contraction in coronary arteries without endothelium, whereas SLIGRL had no effect. Intravenous injection of SFLLRN (1 mg/kg, bolus) into anesthetized rats elicited a transient depressor response followed by pronounced pressor response. In contrast, intravenous administration of SLIGRL (1 mg/kg, bolus) produced only a marked depressor response. Consistent with the in vivo data, SFLLRN contracted the endothelium-rubbed rat aortic rings and aggregated human platelets in vitro, whereas SLIGRL had no effect. The finding that both trypsin and SLIGRL induced endothelium-dependent relaxations indicates the presence of PAR-2 on endothelial cells. In addition, both trypsin and SLIGRL elicited relaxations in thrombin- or SFLLRN-desensitized tissue, suggesting that PAR-2 is distinct from thrombin receptor in vascular endothelium. The lack of PAR-2-mediated platelet aggregation or smooth muscle contraction suggested it might not share the pathogenic properties associated with the thrombin receptor in the vasculature.
Hwa
J J
JJ
Cardiovascular Pharmacology, Schering-Plough Research Institute, Kenilworth, NJ 07033-0530, USA.
Ghibaudi
L
L
Williams
P
P
Chintala
M
M
Zhang
R
R
Chatterjee
M
M
Sybertz
E
E
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D003331:Coronary Vessels / Q000187:drug effects; D010450:Endopeptidases / Q000502:physiology*; D004730:Endothelium, Vascular / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044464:Receptor, PAR-2; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000502:physiology*; D018179:Receptors, Thrombin / Q000502:physiology*; D013552:Swine; D013917:Thrombin / Q000494:pharmacology; D014357:Trypsin / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects
D009842:Oligopeptides; D010446:Peptide Fragments; D044464:Receptor, PAR-2; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; C099570:seryl-leucyl-isoleucyl-glycyl-arginyl-leucine; C082835:thrombin receptor peptide (42-47); D010450:Endopeptidases; D014357:Trypsin; D013917:Thrombin