Thrombin activation of proteinase-activated receptor 1 potentiates the myofilament Ca2+ sensitivity and induces vasoconstriction in porcine pulmonary arteries.
OBJECTIVE
Thrombus formation is commonly associated with pulmonary arterial hypertension (PAH). Thrombin may thus play an important role in the pathogenesis and pathophysiology of PAH. Hence, we investigated the contractile effects of thrombin and its mechanism in pulmonary artery.


METHODS
The cytosolic Ca(2+) concentrations ([Ca(2+)](i)), 20 kDa myosin light chain (MLC20) phosphorylation and tension development were evaluated using the isolated porcine pulmonary artery.


RESULTS
Thrombin induced a sustained contraction in endothelium-denuded strips obtained from different sites of a pulmonary artery, ranging from the main pulmonary artery to the intrapulmonary artery. In the presence of endothelium, thrombin induced a transient relaxation. The contractile effect of thrombin was abolished by either a protease inhibitor or a proteinase-activated receptor 1 (PAR(1)) antagonist, while it was mimicked by PAR(1)-activating peptide (PAR(1)AP), but not PAR(4)AP. The thrombin-induced contraction was associated with a small elevation of [Ca(2+)](i) and an increase in MLC20 phosphorylation. Thrombin and PAR(1)AP induced a greater increase in tension for a given [Ca(2+)](i) elevation than that obtained with high K(+)-depolarization. They also induced a contraction at a fixed Ca(2+) concentration in alpha-toxin-permeabilized preparations.


CONCLUSIONS
The present study revealed a unique property of the pulmonary artery. In contrast to normal arteries of the systemic circulation, thrombin induces a sustained contraction in the normal pulmonary artery, by activating PAR(1) and thereby increasing the sensitivity of the myofilament to Ca(2+). This responsiveness of the pulmonary artery to thrombin may therefore contribute to the pathogenesis and pathophysiology of PAH.
Division of Molecular Cardiology, Research Institute of Angiocardiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Jun
J
Maki
Mayumi
M
Hirano
Sumio
S
Hoka
Hideo
H
Kanaide
Katsuya
K
Hirano
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011651:Pulmonary Artery / Q000378:metabolism; D044463:Receptor, PAR-1 / Q000187:drug effects / Q000378:metabolism*; D013552:Swine; D013917:Thrombin / Q000378:metabolism*; D014661:Vasoconstriction / Q000187:drug effects; D014664:Vasodilation; D054460:rho-Associated Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D018994:Myosin Light Chains; D011480:Protease Inhibitors; D047428:Protein Kinase Inhibitors; D044463:Receptor, PAR-1; D054460:rho-Associated Kinases; D013917:Thrombin; D011188:Potassium