Hamilton J R, Nguyen P B, Cocks T M
Department of Pharmacology, University of Melbourne, Victoria, Australia.
Circ Res. 1998 Jun 29;82(12):1306-11. doi: 10.1161/01.res.82.12.1306.
Protease-activated receptors (PARs) are a family of G protein-coupled receptors activated by a tethered ligand sequence within the amino terminal that are revealed by site-specific proteolysis. The thrombin-sensitive PAR-1 and trypsin-activated PAR-2 mediate endothelium-dependent vascular relaxation in a number of species. Because both thrombin and trypsin-like enzymes have been implicated in coronary artery disease, the purpose of this study was to investigate whether similar receptors are present in human coronary arteries. Thrombin (0.001 to 0.1 U/mL) and trypsin (0.001 to 1 U/mL) caused concentration- and endothelium-dependent relaxations of human coronary artery ring segments suspended in organ chambers for isometric tension recording and contracted with the thromboxane A2 mimetic U46619. These relaxations were dependent on the catalytic activity of each enzyme and were inhibited by the NO synthase inhibitor NG-nitro-L-arginine (100 micromol/L) and the NO scavenger oxyhemoglobin (20 micromol/L). The synthetic PAR-1 tethered ligand sequence SFLLRN-NH2 (0.01 to 10 micromol/L) also caused endothelium-dependent relaxation of U46619-contracted human coronary arteries; however, the equivalent PAR-2 ligand SLIGKV-NH2 caused almost no relaxation. In addition, desensitization to either thrombin or trypsin resulted in cross-desensitization to the other enzyme but had only a minimal affect on the response to SFLLRN-NH2. Therefore, we conclude that human coronary artery endothelial cells possess a PAR-1-like receptor that is potently activated by thrombin, trypsin, and SFLLRN-NH2 to cause NO-mediated vascular relaxation. Once cleaved, this receptor is recycled in a truncated form, able to respond to exogenous application of only its tethered ligand sequence, suggesting the presence of another endogenous activator possibly acting independently of receptor cleavage.
蛋白酶激活受体（PARs）是一类G蛋白偶联受体，其通过氨基末端内的拴系配体序列激活，该序列通过位点特异性蛋白水解而暴露。凝血酶敏感的PAR-1和胰蛋白酶激活的PAR-2在许多物种中介导内皮依赖性血管舒张。由于凝血酶和类胰蛋白酶都与冠状动脉疾病有关，本研究的目的是调查人类冠状动脉中是否存在类似的受体。凝血酶（0.001至0.1 U/mL）和胰蛋白酶（0.001至1 U/mL）引起悬浮在器官腔室中用于等长张力记录并与血栓素A2模拟物U46619收缩的人类冠状动脉环段的浓度依赖性和内皮依赖性舒张。这些舒张依赖于每种酶的催化活性，并被一氧化氮合酶抑制剂NG-硝基-L-精氨酸（100 μmol/L）和一氧化氮清除剂氧合血红蛋白（20 μmol/L）抑制。合成的PAR-1拴系配体序列SFLLRN-NH2（0.01至10 μmol/L）也引起U46619收缩的人类冠状动脉的内皮依赖性舒张；然而，等效的PAR-2配体SLIGKV-NH2几乎没有引起舒张。此外，对凝血酶或胰蛋白酶的脱敏导致对另一种酶的交叉脱敏，但对SFLLRN-NH2的反应影响极小。因此，我们得出结论，人类冠状动脉内皮细胞具有一种PAR-1样受体，其被凝血酶、胰蛋白酶和SFLLRN-NH2有效激活，导致一氧化氮介导的血管舒张。一旦被切割，该受体以截短形式循环利用，仅能对外源施加的其拴系配体序列作出反应，这表明可能存在另一种内源性激活剂，其作用可能独立于受体切割。
