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-Thrombin stimulates contraction of human bronchial rings
by activation of protease-activated receptors
1 Pneumologie der 1. Medizinischen Klinik und Deutsches Herzzentrum, Technische Universität, 81675 Munich, Germany; and 2 Pulmonary and Critical Care Division, University of Pennsylvania, Philadelphia, Pennsylvania 19104-4283
In a variety of
diseases, inflammation causes microvascular leakage and activates
thrombin. Evidence suggests that thrombin increases cytosolic calcium
and stimulates human airway smooth muscle (ASM) cell proliferation. The
receptor subtypes, however, that mediate the effects of thrombin on ASM
cell growth or calcium mobilization remain unknown. In this study, we
postulate that thrombin, which activates specific protease-activated
receptors (PARs), also stimulates contraction of isolated human
bronchial rings. With the use of intact human bronchial rings,
-thrombin (1-20 U/ml) increased bronchial tone to 19 ± 3%
of basal tone (P = 0.008;
n = 5 experiments) and represents 20 ± 8% of the maximum carbachol response. The
EC50 for thrombin-induced force
generation was 12.2 U/ml (95% confidence interval 9.9-15.3 U/ml)
and was not altered in bronchial rings that had the epithelium removed. In parallel experiments, a specific thrombin receptor-activating peptide (TRAP-14; 0.1-100 µmol/l) increased isometric tension to
levels (14 ± 2%; P = 0.0005;
n = 5 experiments) comparable to those
rings stimulated with thrombin. To characterize the receptors that
mediate thrombin effects on human ASM, the expression of PARs in
cultured human ASM cells was analyzed by RT-PCR analysis with specific
primers for PARs. In these cells, PAR1 (thrombin receptor), PAR2, and
PAR3 were expressed at comparable levels. In other experiments using
immunocytochemical staining with specific antibodies to PAR1 and PAR2,
we showed that ASM in bronchial rings and cultured ASM cells express
PAR1 and PAR2 proteins. Taken together, these studies suggest that
-thrombin, in a receptor-specific and dose-dependent manner, induces
contraction of bronchial rings in vitro. In addition, cultured human
ASM cells express mRNA of PAR1, PAR2, and PAR3 and express PAR1 and
PAR2 protein. Further studies are needed to determine whether
-thrombin plays a role in stimulating bronchoconstriction in
inflammatory airway diseases such as asthma and bronchiolitis obliterans.
r-hirudin; thrombin receptor-activating peptide-14; asthma; human bronchi; smooth muscle contraction
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