title: Heterogeneous mechanisms of endothelium-dependent relaxation for thrombin and peptide activators of protease-activated receptor-1 in porcine isolated coronary artery.
abstract: 1. Mechanisms of protease-activated receptor-1 (PAR1)- and PAR2-induced relaxation were investigated in pre-contracted porcine coronary artery ring preparations. 2. Thrombin (0.01 - 0.3 u ml(-1)) and the PAR1-activating peptide SFLLRN (0.1 - 10 microM) caused concentration- and endothelium-dependent relaxation. pEC(50)s (-log u ml(-1) for enzymes, -log M for peptides) and maximum relaxations (R(max), %) for thrombin were 1.8+/-0.1 and 93.5+/-2.8% respectively, and for SFLLRN 6.8+/-0.1 and 90.8+/-1.3%. Similar concentration- and endothelium-dependent relaxations occurred with trypsin (pEC(50) 2.3+/-0.2; R(max) 94.1+/-1.9%) and the PAR2-activating peptide SLIGRL (pEC(50) 6.5+/-0.2; R(max) 92.4+/-1.6%). 3. Relaxations to thrombin, SFLLRN, trypsin and SLIGRL were significantly inhibited (P<0.05) to similar extents by the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (L-NOARG; 100 microM) and the NO scavenger oxyhaemoglobin (20 microM), both separately and in combination. 4. In the presence of the L-type voltage-operated calcium channel (L-VOCC) inhibitor nifedipine (0.3 microM), K(+) (67 mM) abolished the L-NOARG-resistant relaxations to thrombin, SFLLRN, trypsin and SLIGRL. However, nifedipine alone significantly (P<0.05) reduced the pEC(50) (1.5+/-0.1) and R(max) (77.5+/-7.0%) for thrombin but had no effect on relaxations to SFLLRN, trypsin or SLIGRL. Furthermore, L-NOARG-resistant relaxations to thrombin were abolished by nifedipine, whereas relaxations to SFLLRN, trypsin or SLIGRL were not further inhibited by combined treatment with nifedipine and L-NOARG, than they were with L-NOARG treatment alone. 5. Similar selective inhibition of the L-NOARG-resistant relaxation to thrombin, but not SFLLRN, occurred with verapamil (1 microM) and diltiazem (3 microM). 6. Our results suggest heterogeneous mechanisms in the NO-independent relaxation to thrombin and peptide activators of PAR1 in the porcine coronary artery.
authors.affiliation: Department of Pharmacology, University of Melbourne, Victoria 3010, Australia.
authors.forename: J R
authors.initials: JR
authors.lastname: Hamilton
authors.forename: T M
authors.initials: TM
authors.lastname: Cocks
mesh_terms: D000818:Animals; D001685:Biological Factors / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D003331:Coronary Vessels / Q000187:drug effects* / Q000502:physiology; D004730:Endothelium, Vascular; D005260:Female; D006490:Hemostatics / Q000494:pharmacology; D008297:Male; D009569:Nitric Oxide / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin / Q000187:drug effects* / Q000502:physiology; D013552:Swine; D013917:Thrombin / Q000494:pharmacology; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
chemical_list: D001685:Biological Factors; D002121:Calcium Channel Blockers; D006490:Hemostatics; D044463:Receptor, PAR-1; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin; C067410:endothelium-dependent hyperpolarization factor; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; D013917:Thrombin