Trottier Greg, Hollenberg Morley, Wang Xuemei, Gui Yu, Loutzenhiser Kathy, Loutzenhiser Rodger
Smooth Muscle Research Group, Department of Pharmacology and Therapeutics, University of Calgary, Calgary, Alberta, Canada T2N 4N1.
Am J Physiol Renal Physiol. 2002 May;282(5):F891-7. doi: 10.1152/ajprenal.00233.2001.
Proteinase-activated receptors (PARs) are a novel class of G protein-coupled receptors that respond to signals through endogenous proteinases. PAR activation involves enzymatic cleavage of the extracellular NH(2)-terminal domain and unmasking of a new NH(2) terminus, which serves as an anchored ligand to activate the receptor. At least four PAR subtypes have been identified. In the present study, we used the in vitro perfused hydronephrotic rat kidney to examine the effects of activating PAR-2 on the afferent arteriole. The synthetic peptide SLIGRL-NH(2), which corresponds to the exposed ligand sequence and selectively activates PAR-2, did not alter basal afferent arteriolar diameter but caused a concentration-dependent vasodilation (3-30 microM) of arterioles preconstricted by angiotensin II (0.1 nM). A modified peptide sequence (LSIGRL-NH(2), inactive at PAR-2) had no effect. This vasodilation was characterized by an initial transient component followed by a smaller sustained response. A similar pattern of vasodilation was seen when SLIGRL-NH(2) was administered to isolated perfused normal rat kidney. The sustained component of the PAR-2-induced afferent arteriolar vasodilation was eliminated by nitric oxide (NO) synthase inhibition (100 microM nitro-L-arginine methyl ester). In contrast, the transient vasodilation persisted under these conditions. This transient response was not observed when afferent arterioles were preconstricted with elevated KCl, suggesting involvement of an endothelium-derived hyperpolarizing factor. Finally, RT-PCR revealed the presence of PAR-2 mRNA in isolated afferent arterioles. These findings indicate that PAR-2 is expressed in the afferent arteriole and that its activation elicits afferent arteriolar vasodilation by NO-dependent and NO-independent mechanisms.
蛋白酶激活受体（PARs）是一类新型的G蛋白偶联受体，可通过内源性蛋白酶对信号作出反应。PAR的激活涉及细胞外NH₂末端结构域的酶促裂解以及新NH₂末端的暴露，该末端作为锚定配体激活受体。已鉴定出至少四种PAR亚型。在本研究中，我们使用体外灌注的肾积水大鼠肾脏来研究激活PAR-2对入球小动脉的影响。合成肽SLIGRL-NH₂，其对应于暴露的配体序列并选择性激活PAR-2，并未改变基础入球小动脉直径，但导致由血管紧张素II（0.1 nM）预收缩的小动脉出现浓度依赖性血管舒张（3-30 μM）。修饰后的肽序列（LSIGRL-NH₂，对PAR-2无活性）无作用。这种血管舒张的特征是最初的瞬时成分，随后是较小的持续反应。当将SLIGRL-NH₂施用于分离的灌注正常大鼠肾脏时，观察到类似的血管舒张模式。PAR-2诱导的入球小动脉血管舒张的持续成分通过一氧化氮（NO）合酶抑制（100 μM硝基-L-精氨酸甲酯）而消除。相反，在这些条件下瞬时血管舒张持续存在。当入球小动脉用升高的KCl预收缩时未观察到这种瞬时反应，提示内皮源性超极化因子参与其中。最后，RT-PCR显示在分离的入球小动脉中存在PAR-2 mRNA。这些发现表明PAR-2在入球小动脉中表达，并且其激活通过NO依赖性和NO非依赖性机制引起入球小动脉血管舒张。
