[Show abstract][Hide abstract] ABSTRACT: Since protease-activated receptors (PARs) are distributed throughout the gastrointestinal tract, we investigated the role of PARs in modulation of the motility of the rat oesophageal muscularis mucosae.
Thrombin produced contraction of segments of the upper and lower part of the smooth muscle. Trypsin contracted both the muscle preparations only at high concentrations. SFLLR-NH2 and TFLLR-NH2 (PAR-1-activating peptides), but not the PAR-1-inactive peptide FSLLR-NH2, evoked a marked contraction. In contrast, the PAR-2 agonist SLIGRL-NH2 and the PAR-4 agonist GYPGKF-NH2 caused no or only a negligible contraction.
In oesophageal preparations precontracted with carbachol, thrombin produced a dual action i.e. relaxation followed by contraction. TFLLR-NH2 further contracted the precontracted preparations with no preceding relaxation. GYPGKF-NH2, but not the inactive peptide GAPGKF-NH2, produced marked relaxation. Trypsin or SLIGRL-NH2 caused no relaxation.
The PAR-1-mediated contraction was completely abolished in Ca2+-free medium and considerably attenuated by nifedipine (1 μM) and in a low Na+ medium. The PAR-4-mediated relaxation was resistant to tetrodotoxin (10 μM), apamin (0.1 μM), charybdotoxin (0.1 μM), L-NG-nitroarginine methyl ester (100 μM), indomethacin (3 μM), propranolol (5 μM) or adenosine 3′,5′-cyclic monophosphorothioate, 8-bromo, Rp-isomer (30 μM).
Thus, thrombin plays a dual role in modulating the motility of the oesophageal muscularis mucosae, producing contraction via PAR-1 and relaxation via PAR-4. The PAR-1-mediated effect appears to occur largely through increased Na+ permeability followed by activation of L-type Ca2+ channels and subsequent influx of extracellular Ca2+. Our data could provide evidence for a novel role of PAR-4 as opposed to PAR-1, although the underlying mechanisms are still open to question.
British Journal of Pharmacology (2000) 131, 578–584; doi:10.1038/sj.bjp.0703590
Full-text · Article · Jan 2009 · British Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Protease-activated receptor (PAR)-4 is a recently identified low-affinity thrombin receptor that plays a pathophysiological role in many types of tissues including the lung. Here, we showed for the first time that PAR4 mRNA and protein are expressed on primary cultured mouse lung alveolar epithelial cells by reverse transcriptase-polymerase chain reaction (RT-PCR) and immunocytochemical analyses. In a fura 2-AM-loaded single epithelial cell, stimulation with thrombin (1 U/ml) and a PAR4 agonist peptide (AYPGKF-NH(2), 1-100 microM) increased intracellular Ca(2+) concentration ([Ca(2+)](i)), which consisted of an initial peak phase followed by a slowly decaying delayed phase, while a PAR1 agonist peptide, TFLLR-NH(2) (1-100 microM), induced a transient increase in [Ca(2+)](i). AYPGKF-NH(2) (10 microM)-induced [Ca(2+)](i) response was attenuated by a PAR4 antagonist peptide (tcY-NH(2)), a phospholipase C inhibitor, U-73122 (1-10 microM) or a Ca(2+)-ATPase inhibitor, thapsigargin (1 microM). Removal of extracellular Ca(2+) or an inhibitor of store-operated Ca(2+) entry, trans-resveratrol (1 microM) shortened the time to shut off the Ca(2+) response without any significant effects on the magnitude of the peak [Ca(2+)](i). Thus, stimulation of PAR4 appeared to mobilize Ca(2+) from intracellular stores in the initial peak response and to enhance Ca(2+) entry through the store depletion-operated pathway in the delayed phase. The latter mechanism probably contributed to the longer responsiveness of PAR4 stimulation.
[Show abstract][Hide abstract] ABSTRACT: Proteinase-activated receptors (PARs; PAR1-4) that can be activated by serine proteinases such as thrombin and neutrophil catepsin G are known to contribute to the pathogenesis of various pulmonary diseases including fibrosis. Among these PARs, especially PAR4, a newly identified subtype, is highly expressed in the lung. Here, we examined whether PAR4 stimulation plays a role in the formation of fibrotic response in the lung, through alveolar epithelial-mesenchymal transition (EMT) which contributes to the increase in myofibroblast population.
EMT was assessed by measuring the changes in each specific cell markers, E-cadherin for epithelial cell, alpha-smooth muscle actin (alpha-SMA) for myofibroblast, using primary cultured mouse alveolar epithelial cells and human lung carcinoma-derived alveolar epithelial cell line (A549 cells).
Stimulation of PAR with thrombin (1 U/ml) or a synthetic PAR4 agonist peptide (AYPGKF-NH2, 100 muM) for 72 h induced morphological changes from cobblestone-like structure to elongated shape in primary cultured alveolar epithelial cells and A549 cells. In immunocytochemical analyses of these cells, such PAR4 stimulation decreased E-cadherin-like immunoreactivity and increased alpha-SMA-like immunoreactivity, as observed with a typical EMT-inducer, tumor growth factor-beta (TGF-beta). Western blot analyses of PAR4-stimulated A549 cells also showed similar changes in expression of these EMT-related marker proteins. Such PAR4-mediated changes were attenuated by inhibitors of epidermal growth factor receptor (EGFR) kinase and Src. PAR4-mediated morphological changes in primary cultured alveolar epithelial cells were reduced in the presence of these inhibitors. PAR4 stimulation increased tyrosine phosphorylated EGFR or tyrosine phosphorylated Src level in A549 cells, and the former response being inhibited by Src inhibitor.
PAR4 stimulation of alveolar epithelial cells induced epithelial-mesenchymal transition (EMT) as monitored by cell shapes, and epithelial or myofibroblast marker at least partly through EGFR transactivation via receptor-linked Src activation.
Preview · Article · Feb 2007 · Respiratory research
[Show abstract][Hide abstract] ABSTRACT: Proteinase-activated receptor-1 (PAR1), a G protein-coupled receptor (GPCR) for thrombin, can be activated not only by PAR1-activating peptides (PAR1APs) based on the N-terminal cryptic tethered ligand sequence but also by an N-palmitoylated (Pal) peptide, Pal-RCLSSSAVANRSKKSRALF-amide (P1pal-19), based on the intracellular loop 3 of PAR1, designated pepducin, in human platelets or PAR1-transfected cells. The present article evaluated the actions of P1pal-19 and also the shorter peptide, Pal-RCLSSSAVANRS-amide (P1pal-12), known as a possible PAR1 antagonist, in multiple cells/tissues that naturally express PAR1. P1pal-19 as well as a PAR1AP, TFLLR-amide, evoked cytosolic Ca(2+) mobilization in cultured human lung epithelial cells (A549) and rat gastric mucosal epithelial cells (RGM1). P1pal-19 and TFLLR-amide, but not a PAR2-activating peptide, SLIGRL-amide, caused delayed prostaglandin E(2) formation in RGM1 cells. P1pal-19, like TFLLR-amide, produced endothelial NO-dependent relaxation in rat aorta and epithelial prostanoid-dependent relaxation in mouse bronchus. The P1pal-19-induced relaxation remained constant even after desensitization of PAR1 with TFLLR-amide in either tissue. P1pal-19 failed to mimic the contractile effects of TFLLR-amide in the endothelium-denuded preparations of rat aorta or superior mesenteric artery and the rat gastric longitudinal smooth muscle strips. P1pal-12 partially inhibited the vasorelaxation caused by TFLLR-amide and P1pal-19, but not SLIGRL-amide, in the rat aorta. Our data thus indicate that P1pal-19 is capable of mimicking the effects of PAR1APs in the endothelial and epithelial, but not smooth muscle, cells/tissues, and suggest that P1pal-12 may act as a PAR1 antagonist in the vascular endothelium.
No preview · Article · Jan 2007 · Annals of the New York Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: Protease-activated receptor 2 (PAR2) has been implicated in the pathogenesis of airway inflammation. We report that epithelial PAR2 stimulation with trypsin (0.05-1 U/ml) or an agonist peptide (SLIGKV-NH2, 1-100 microM) for 0.5-3 h dose- and time-dependently enhanced neutrophil adhesion to alveolar type II epithelial cells (A549 cells) and that this stimulation also induced the formation of epithelial actin filaments. Both responses in neutrophil adhesion and epithelial actin reorganization were reduced by a Rho inhibitor, mevastatin and by a Rho-associated kinase (ROCK) inhibitor, Y-27632 ((R)-(+)-trans-N-(4-Pyridyl)-4-(1-aminoethyl)-cyclohexanecarboxamide). Neutrophil adherence was also inhibited by an inhibitor of actin polymerization, cytochalasin D and a tyrosine kinase inhibitor, genistein. Further, the PAR2-mediated tyrosine phosphorylation of focal adhesion kinase (FAK), a major cytoskeleton protein, was detected, and this response was inhibited by mevastatin or Y-27632. These results suggest that PAR2 stimulation of alveolar epithelial cells enhances neutrophil adhesion presumably at least in part through Rho/ROCK signal-mediated actin cytoskeleton reorganization associated with the tyrosine phosphorylation of FAK.
No preview · Article · May 2006 · European Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Protease-activated receptor-2 (PAR-2) plays an extensive role in the regulation of digestive exocrine secretion. The present study examined whether PAR-2-related peptides could modulate tear secretion in rats and analyzed the underlying mechanisms. SLIGRL-NH(2), a PAR-2-activating peptide (PAR-2-AP) derived from mouse/rat PAR-2, when administered i.v. in combination with amastatin, an aminopeptidase inhibitor, evoked tear secretion, whereas LRGILS-NH(2), a PAR-2-inactive reversed peptide, had no such effect. In contrast, LSIGRL-NH(2), a partially reversed peptide known to be inactive with PAR-2, caused tear secretion equivalent to the effect of SLIGRL-NH(2). SLIGKV-NH(2), a human-derived PAR-2-AP, also induced significant tear secretion though to a lesser extent, whereas neither VKGILS-NH(2), a reversed peptide, nor LSIGKV-NH(2), a partially reversed peptide, produced any secretion. In desensitization experiments, after the first dose of SLIGRL-NH(2), the second dose of SLIGRL-NH(2) produced no tear secretion, whereas the response to LSIGRL-NH(2) was only partially inhibited by preadministration of SLIGRL-NH(2). Preadministration of LSIGRL-NH(2) abolished the response to subsequently administered LSIGRL-NH(2) but not SLIGRL-NH(2). The tear secretion induced by LSIGRL-NH(2) but not by PAR-2-APs was blocked by atropine or hexamethonium. Mast cell depletion due to repeated doses of compound 48/80 did not alter the effect of SLIGRL-NH(2) or LSIGRL-NH(2). Finally, IGRL-NH(2), a possible core structure of LSIGRL-NH(2), triggered tear secretion in an atropine-reversible manner. Our findings suggest that the PAR-2-APs SLIGRL-NH(2) and SLIGKV-NH(2) cause tear secretion, most likely via PAR-2 and that LSIGRL-NH(2), a PAR-2-inactive peptide, and IGRL-NH(2), its key structure, trigger tear secretion by stimulating parasympathetic nerves via an unidentified target molecule.
Preview · Article · Feb 2005 · Journal of Pharmacology and Experimental Therapeutics
[Show abstract][Hide abstract] ABSTRACT: Receptor-activating peptides for protease-activated receptors (PARs) 1 or 2 enhance gastric mucosal blood flow (GMBF) and protect against gastric mucosal injury in rats. We thus examined and characterized the effects of PAR-1 and PAR-2 agonists on the isometric tension in isolated rat gastric artery. The agonists for PAR-2 or PAR-1 produced vasodilation in the endothelium-intact arterial rings, which was abolished by removal of the endothelium. The mechanisms underlying the PAR-2- and PAR-1-mediated relaxation involved NO, endothelium-derived hyperpolarizing factor (EDHF) and prostanoids, to distinct extent, as evaluated by use of inhibitors of NO synthase, cyclo-oxygenase and Ca2+-activated K+ channels. The EDHF-dependent relaxation responses were significantly attenuated by gap junction inhibitors. These findings demonstrate that endothelial PAR-1 and PAR-2, upon activation, dilate the gastric artery via NO and prostanoid formation and also EDHF mechanisms including gap junctions, which would enhance GMBF.
[Show abstract][Hide abstract] ABSTRACT: On activation, protease-activated receptor (PAR)-2 modulates multiple gastric functions and exerts mucosal protection via activation of sensory neurons. The role of PAR-1, a thrombin receptor, in the stomach remains unknown. We thus examined if the PAR-1 agonist could protect against gastric mucosal injury in rats.
Gastric mucosal injury was created by oral administration of ethanol/HCl or absolute ethanol in conscious rats. Gastric mucosal blood flow and acid secretion were determined in anesthetized rats. Immunohistochemical analyses of PAR-1 and cyclooxygenase (COX)-1 were also performed in rat and human stomach.
The PAR-1 agonist TFLLR-NH(2), administered intravenously in combination with amastatin, protected against the gastric mucosal injury induced by ethanol/HCl or absolute ethanol. The protective effect of TFLLR-NH(2) was abolished by indomethacin or a COX-1 inhibitor but not by ablation of sensory neurons with capsaicin. TFLLR-NH(2) produced an NO-independent increase in gastric mucosal blood flow that was partially inhibited by blockade of the endothelium-derived hyperpolarizing factor pathway. This inhibitory effect was promoted by indomethacin. TFLLR-NH(2) suppressed carbachol-evoked acid secretion in an indomethacin-reversible manner. Immunoreactive PAR-1 and COX-1 were expressed abundantly in rat gastric muscularis mucosae and smooth muscle, and the former protein was also detectable in blood vessels. Similar staining was observed in human gastric muscularis mucosae.
The PAR-1 agonist, given systemically, protects against gastric mucosal injury via COX-1-dependent formation of prostanoids, modulating multiple gastric functions. Our data identify a novel protective role for PAR-1 in gastric mucosa, and the underlying mechanism is entirely different from that for PAR-2.
No preview · Article · Feb 2004 · Gastroenterology
[Show abstract][Hide abstract] ABSTRACT: E-cadherin is one of the cell adhesion molecules normally expressed on epithelial cells. We previously reported that murine bone marrow-derived mast cells express E-cadherin that could be involved in homophilic binding with epithelial cell E-cadherin. In the present study we examined whether E-cadherin is also expressed in human mast cell HMC-1. Gene expression of E-cadherin and beta-catenin was observed in HMC-1 by reverse transcription-polymerase chain reaction (RT-PCR), while N-cadherin expression was undetectable. cDNA sequencing of HMC-1 E-cadherin revealed no deletions or mutations. E-cadherin expression in HMC-1 was confirmed by immunoblotting as well as by flow cytometric analyses. In the presence of E-cadherin blocking antibody or a synthetic E-cadherin decapeptide with HAV sequence in culture medium, adhesion of HMC-1 cells to the A431 epithelial cell monolayer was slightly but significantly suppressed. In contrast, N- or P-cadherin decapeptides did not suppress the binding. These results indicated that human mast cell HMC-1 expresses E-cadherin, and is possibly involved in cellular interactions with epithelial cells, while other functions still remain to be elucidated.
[Show abstract][Hide abstract] ABSTRACT: Agonists for protease-activated receptor-2 (PAR-2) cause hypotension and an increase in gastric mucosal blood flow (GMBF) in vivo. We thus studied the mechanisms underlying the circulatory modulation by PAR-2 activation in vivo, especially with respect to involvement of endothelium-derived hyperpolarizing factor (EDHF).
Arterial blood pressure and GMBF were measured in anesthetized rats in vivo. Vascular relaxation was assessed in the precontracted rat gastric arterial rings in vitro.
The PAR-2-activating peptide SLIGRL-NH2 and/or trypsin, administered i.v., produced largely NO-independent hypotension and increase in GMBF accompanied by decreased gastric mucosal vascular resistance (GMVR) in rats.
Combined administration of apamin and charybdotoxin, but not each of them, specifically abolished the hypotension, increased GMBF and decreased GMVR caused by the PAR-2 agonists.
In the isolated rat gastric artery, SLIGRL-NH2 elicited endothelium-dependent relaxation even in the presence of an NO synthase inhibitor and indomethacin, which was abolished by apamin plus charybdotoxin.
Our data suggest involvement of apamin/charybdotoxin-sensitive K+ channels in the PAR-2-triggered hypotension and increased GMBF, predicting a role of EDHF-like factors.
British Journal of Pharmacology (2003) 140, 247–254. doi:10.1038/sj.bjp.0705433
Full-text · Article · Oct 2003 · British Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Protease-activated receptor-2, a G protein-coupled receptor activated by serine proteases such as trypsin, tryptase and coagulation factors VIIa and Xa, modulates pancreatic and salivary exocrine secretion. In the present study, we examined the distribution of PAR-2 in the pancreas and parotid gland, and characterized the PAR-2-mediated secretion of amylase by these tissues in vivo. Immunohistochemical analyses using the polyclonal antibody against rat PAR-2 clearly showed abundant expression of PAR-2 in rat pancreatic and parotid acini. The PAR-2 agonist SLIGRL-NH2, administered intraperitoneally (i.p.) at 1-10 micromol/kg and 1.5-15 micromol/kg, in combination with amastatin, an aminopeptidase inhibitor, facilitated in vivo secretion of pancreatic and salivary amylase in a dose-dependent manner, respectively, in the mouse. The PAR-2-mediated secretion of pancreatic amylase was abolished by pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor. The secretion of salivary amylase in response to the PAR-2 agonist at a large dose, 15 micromol/kg, but not at a smaller dose, 5 micromol/kg, was partially reduced by L-NAME. Pretreatment with capsaicin for ablation of the sensory neurons did not modify the PAR-2-mediated secretion of pancreatic and salivary amylase in the mouse. In conclusion, our study demonstrates expression of PAR-2 in rat pancreatic acini as well as parotid acini and indicates that nitric oxide participates in the PAR-2-mediated in vivo secretion of pancreatic amylase, and, to a certain extent, of salivary amylase, although capsaicin-sensitive sensory neurons, known to be activated by PAR-2, are not involved in the evoked pancreatic or salivary amylase secretion.
[Show abstract][Hide abstract] ABSTRACT: Activation of protease-activated receptor-2 (PAR-2), a receptor activated by trypsin/tryptase, induces neurally mediated gastric mucus secretion accompanied by mucosal cytoprotection. In the present study, we investigated whether PAR-2 could modulate gastric acid secretion in rats. Messenger RNAs for PAR-2 and PAR-1 were detected in the gastric mucosa and smooth muscle. The PAR-2-activating peptide SLIGRL-NH(2), but not the inactive control peptide, when administered i.v., strongly suppressed gastric acid secretion in response to carbachol, pentagastrin or 2-deoxy-D-glucose in the rats with a pylorus ligation. The PAR-2-mediated suppression of acid secretion was resistant to cyclooxygenase inhibition or ablation of sensory neurons by capsaicin. Our results provide novel evidence that in addition to stimulating neurally mediated mucus secretion, activation of PAR-2 suppresses gastric acid secretion independently of prostanoid production or sensory neurons. These dual actions of PAR-2 would result in gastric mucosal cytoprotection.
No preview · Article · Jul 2002 · European Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Agonists of protease-activated receptor-2 (PAR-2) trigger neurally mediated mucus secretion accompanied by mucosal cytoprotection in the stomach. The present study immunolocalized PAR-2 in the rat gastric mucosa and examined if PAR-2 could modulate pepsin/pepsinogen secretion in rats.
PAR-2-like immunoreactivity was abundant in the deep regions of gastric mucosa, especially in chief cells.
The PAR-2 agonist SLIGRL-NH2, but not the control peptide LSIGRL-NH2, administered i.v. repeatedly at 0.3 – 1 μmol kg−1, four times in total, significantly facilitated gastric pepsin secretion, although a single dose produced no significant effect.
The PAR-2-mediated gastric pepsin secretion was resistant to omeprazole, NG-nitro-L-arginine methyl ester (L-NAME) or atropine, and also to ablation of sensory neurons by capsaicin.
Our study thus provides novel evidence that PAR-2 is localized in mucosal chief cells and facilitates gastric pepsin secretion in the rats, most probably by a direct mechanism.
British Journal of Pharmacology (2002) 135, 1292–1296; doi:10.1038/sj.bjp.0704562
Full-text · Article · Apr 2002 · British Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Protease-activated receptors (PARs) 1 and 2 modulate the gastric and intestinal smooth muscle motility in vitro. In the present study, we examined if activation of PAR-2 and PAR-1 could alter gastrointestinal transit in mice.
Intraperitoneal administration of the PAR-2-activating peptide SLIGRL-NH2, but not the inactive control LSIGRL-NH2, at 1–5 μmol kg−1, in combination with the aminopeptidase inhibitor amastatin at 2.5 μmol kg−1, facilitated gastrointestinal transit in a dose-dependent manner. The human PAR-1-derived peptide SFLLR-NH2 and the specific PAR-1 agonist TFLLR-NH2, but not the inactive control FSLLR-NH2, at 2.5–10 μmol kg−1, in combination with amastatin, also promoted gastrointestinal transit.
The Ca2+-activated, small conductance K+ channel inhibitor apamin at 0.01 μmol kg−1 significantly potentiated the actions of SLIGRL-NH2 and TFLLR-NH2 at subeffective doses.
The increased gastrointestinal transit exerted by either SLIGRL-NH2 at 5 μmol kg−1 or TFLLR-NH2 at 10 μmol kg−1 was completely abolished by the L-type Ca2+ channel inhibitor verapamil at 61.6 μmol kg−1. In contrast, the tyrosine kinase inhibitor genistein at 18.5 μmol kg−1 failed to modify the effects of the agonists for PAR-2 or PAR-1.
These findings demonstrate that PAR-1 and PAR-2 modulate gastrointestinal transit in mice in vivo. Our data also suggest that the PAR-1-and PAR-2-mediated effects are modulated by apamin-sensitive K+ channels and are dependent on activation of L-type Ca2+ channels, but independent of tyrosine kinase. Our study thus provides novel evidence for the physiological and/or pathophysiological roles of PARs 1 and 2 in the digestive systems, most probably during inflammation.
British Journal of Pharmacology (2001) 133, 1213–1218; doi:10.1038/sj.bjp.0704211
Full-text · Article · Jul 2001 · British Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Protease-activated receptor-2 (PAR-2) and/or effector cell protease receptor-1 (EPR-1) may mediate the direct cellular actions of coagulation factor Xa in some cultured cell lines. The present study examined if factor Xa could actually evoke relaxation through either of these receptor systems in isolated rat aorta. Factor Xa at 8.5-85 nM, like the PAR-2-activators trypsin and SLIGRL-NH(2), produced nitric oxide-dependent relaxation in the precontracted aortic rings. PAR-2 desensitization abolished relaxation responses to factor Xa as well as trypsin in the rings. The factor Xa interepidermal growth factor synthetic peptide L(83)FTRKL(88)(G)-NH(2), known to block factor Xa binding to EPR-1, failed to inhibit factor Xa-evoked relaxation in the preparations. Our findings provide evidence that factor Xa evokes relaxation by activating PAR-2, but independently of EPR-1, in the rat aorta. The factor Xa-PAR-2 pathway might thus contribute to the severe hypotension during sepsis, in which multiple coagulation factors including factor X would become activated and PAR-2 would be induced.
No preview · Article · Apr 2001 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Activation of protease-activated receptor-1 (PAR-1) produces a dual action, apamin-sensitive relaxation followed by contraction, in the rat duodenal smooth muscle, which is partially dependent on activation of L-type Ca2+ channels, protein kinase C (PKC) or tyrosine kinase (TK), and resistant to tetrodotoxin. The present study further characterized the PAR-1-mediated duodenal responses. Removal of extracellular Ca2+ as well as SK&F96365 reduced the contraction due to the PAR-1 agonist TFLLR-NH2 (TFp-NH2) by 60-80% that was similar to the extent of the inhibition by nifedipine. Lowering of the extracellular Na+ concentration, but not IAA-94, a Cl- channel inhibitor, reduced both the PAR-1-mediated contraction and relaxation by about 50%. U73122, a phospholipase C (PLC) inhibitor, or wortmannin, a phosphatidyl inositol 3'-kinase (PI3K) inhibitor, significantly reduced the PAR-1-mediated contraction, but not the relaxation, by itself, as the PKC inhibitor GF109203X and the TK inhibitor genistein did. U73122 or wortmannin, like GF109203X, when applied in combination with genistein, significantly reduced the PAR-1-mediated relaxation. The relaxation was resistant to antagonists of PACAP receptors, VIP receptors and P2 purinoceptors. Thus, the PAR-1-mediated contraction is considered to be dependent on intracellular and extracellular Ca2+, the influx of the latter being induced through activation of L-type Ca2+ channels triggered by the enhanced Na+ permeability, and that PLC and PI3K, in addition to PKC and TK, are involved in the PAR-1-mediated dual responses. Furthermore, non-adrenergic, non-cholinergic nerve neurotransmitter candidates that may modulate K+ channels do not appear to contribute to the relaxation by PAR-1 activation.
[Show abstract][Hide abstract] ABSTRACT: Proteinase-activated receptor-2 (PAR-2) is expressed throughout the gastrointestinal tract including the pancreas, and may be involved in digestive functions. The aim of our study was to evaluate a potential role for PAR-2 in regulating salivary and pancreatic exocrine secretion in vivo.
PAR-2-activating peptides (PAR-2-APs), but not selective PAR-1-APs, administered intravenously, increased salivary secretion in the mouse or rat; this effect of the PAR-2-APs was unaffected by atropine, phentolamine, propranolol or indomethacin.
Secretion (amylase) by rat parotid gland slices in vitro was also stimulated by PAR-2-APs and trypsin, but not by activation of other PARs.
PAR-2-APs, administered to rats in vivo, caused a prompt effect on pancreatic exocrine secretion.
PAR-2 mRNA, known to be present in pancreatic tissue, was also detected in parotid tissue.
Our results indicate that in addition to a potential role in regulating cardiovascular and respiratory functions, PAR-2 may also play a general role in vivo for the direct regulation of glandular exocrine secretion.
British Journal of Pharmacology (2000) 129, 1808–1814; doi:10.1038/sj.bjp.0703274
Full-text · Article · Mar 2000 · British Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: Activation of protease-activated receptor (PAR)-1 or PAR-2 elicits inflammation most probably via mast cell degranulation in vivo. The present study aimed at characterizing PARs in rat peritoneal mast cells (PMC). Messenger RNA for PAR-1, but not for PAR-2, was detected in PMC. Thrombin, the PAR-1 agonist SFLLR-NH2 or the PAR-2 agonist SLIGRL-NH2 failed to induce histamine release from PMC. Surprisingly, the PAR-2-inactive control peptide LSIGRL-NH2 triggered histamine release from PMC. Thus, PAR-1, but not PAR-2, are expressed in PMC, whereas neither PAR-1 nor PAR-2 are considered to be involved in degranulation of PMC. LSIGRL-NH2 does not appear to be appropriate as a control peptide for PAR-2 in inflammation studies.
No preview · Article · Feb 2000 · The Japanese Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: The present study examined effects of agonist enzymes and receptor-activating peptides for protease-activated receptors (PARs) on duodenal motility in the rat, and also investigated possible mechanisms underlying the evoked responses.
Thrombin at 0.03–0.1 μM and the PAR-1-activating peptide SFLLR-NH2 at 3–100 μM or TFLLR-NH2 at 10–50 μM produced a dual action, relaxation followed by contraction of the duodenal longitudinal muscle. The PAR-2-activating peptide SLIGRL-NH2 at 10–100 μM elicited only small contraction. Trypsin at 0.08 μM induced small contraction, or relaxation followed by contraction, depending on preparations. The PAR-4-activating peptide GYPGKF-NH2 at 1000 μM exhibited no effect.
The contractile responses of the duodenal strips to TFLLR-NH2 and to SLIGRL-NH2 were partially attenuated by the L-type calcium channel blocker nifedipine (1 μM), the protein kinase C inhibitor GF109203X (1 μM) and the tyrosine kinase inhibitor genistein (15 μM), but were resistant to indomethacin (3 μM) and tetrodotoxin (1–10 μM).
The relaxation of the preparations exerted by TFLLR-NH2 was unaffected by indomethacin (3 μM), propranolol (5 μM), NG-nitro-L-arginine methyl ester (100 μM) and tetrodotoxin (1–10 μM). This relaxation was resistant to either GF109203X (1 μM) or genistein (15 μM), but was, remarkably, attenuated by combined application of these two kinase inhibitors.
Apamin (0.1 μM), an inhibitor of calcium-activated, small-conductance potassium channels, but not charybdotoxin (0.1 μM), completely abolished the PAR-1-mediated duodenal relaxation, and significantly enhanced the PAR-1-mediated contraction.
These findings demonstrate that PAR-1 plays a dual role, suppression and facilitation of smooth muscle motility in the rat duodenum, while PAR-2 plays a minor excitatory role in the muscle, and that PAR-4 is not involved in the duodenal tension modulation. The results also suggest that the contractile responses to PAR-1 and PAR-2 activation are mediated, in part, by activation of L-type calcium channels, protein kinase C and tyrosine kinase, and that the relaxation response to PAR-1 activation occurs via activation of apamin-sensitive, but charybdotoxin-insensitive, potassium channels, in which both protein kinase C and tyrosine kinase might be involved synergistically.
British Journal of Pharmacology (1999) 128, 865–872; doi:10.1038/sj.bjp.0702755
Full-text · Article · Sep 1999 · British Journal of Pharmacology