Endothelins are thought to act through two specific, plasmalemmal G protein-coupled receptor subtypes, ET A R and ET B R. However, in subfractionated cardiac membranes, ET A R immunoreactivity was detected only in the plasma membrane whereas ET B R immunoreactivity was detected predominantly in membranes of intracellular origin. Confocal microscopy demonstrated the presence of intracellular ET A R and ET B R in ventricular myocytes. ET A R were primarily on plasma membrane (surface membranes and transverse-tubules) and to a lesser extent on the nucleus while ET B R localized primarily to the nuclei. Western blot analysis of nuclei isolated from the heart indicated the presence of endothelin receptors: both ET A R and ET B R copurified with nucleoporin 62, whereas markers of endoplasmic reticulum and Golgi membranes were depleted. Endothelins are a family of 21-amino acid isopeptides (ET-1, -2, and -3), 1 derived from different genes, which mediate a wide spectrum of pharmacological activities in a variety of tissues (see Ref. 1). In the heart, ET-1 produces positive inotropic (2-4) and chronotropic (5) effects, prolongs the action potential (6, 7), and mediates cardiac remodeling in hypertrophy (4, 8 -14), myocardial infarction (15), and congestive heart failure (16, 17). To date, two mammalian endothelin receptor subtypes (ET A R and ET B R) have been cloned (18 -20). The ET A R is selective for ET-1 ϭ ET-2 Ͼ Ͼ ET-3, with sarafotoxin 6c being inactive whereas the ET B R is non-selective. Subtype-specific pharmacological antagonists also help to distinguish the two receptor subtypes. An additional endothelin receptor (ETR) subtype, ET C R, has been cloned from Xenopus laevis (21); however, a mammalian homolog has yet to be identified. Both ET A R and ET B R are seven-transmembrane spanning receptors known to couple to an overlapping array of heterotrimeric G-proteins (22) leading to activation of multiple signaling systems including phospholipase C (23-25), phospholipase D (26, 27), phospholipase A 2 (28), cytosolic Ca 2ϩ (29, 30), Na/H exchange (31), cAMP production (23), cGMP production (32), tyrosine kinases (33, 34), and mitogen-activated protein kinases (14,35,36). Both ET A R and ET B R subtypes are present in heart (18,19,(37)(38)(39); in human myocardium, ET A R and ET B R are expressed at similar levels (38).It is now thought that ET-1 may act in an autocrine/paracrine manner in the cardiac ventricular myocyte. All three endothelins are synthesized as larger precursor proteins, prepro-ETs, which are subsequently cleaved to 37-41-amino acid proforms, referred to as big endothelins. Big endothelins are converted to mature endothelins by endothelin-converting enzymes (ECE). Splice variants of the ECE-1 isoform, ECE-1a and ECE-1c, have been detected in adult cardiac myocytes (40), and ECE-1c expression is up-regulated 5-fold in myocytes during congestive heart failure (40). ET-1 is produced, stored, and secreted by neonatal (41) and adult cardiac ventricular myocytes (42) under basal conditions, and regulat...

This study sought to assess putative pathways involved in the anti-inflammatory effects of 17,18-epoxyeicosatetraenoic acid (17,18-EpETE), as measured by a decrease in the contractile reactivity and Ca(2+) sensitivity of TNF-α-pretreated human bronchi. Tension measurements performed in the presence of 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), a soluble epoxide hydrolase (sEH)-specific inhibitor, demonstrated that 17,18-EpETE reduced the reactivity of TNF-α-pretreated tissues. The overexpression of sEH detected in patients with asthma and TNF-α-treated bronchi contributed to the maintenance of hyperresponsiveness in our models, which involved intracellular proinflammatory cascades. The inhibition of peroxisome proliferator-activated receptor (PPAR)γ by GW9662 abolished 17,18-EpETE + AUDA-mediated anti-inflammatory effects by inducing IκBα degradation and cytokine synthesis, indicating that PPARγ is a molecular target of epoxy-eicosanoids. Western blot analysis revealed that 17,18-EpETE pretreatment reversed the phosphorylation of p38 mitogen-activated protein kinase (p38-MAPK) induced by TNF-α in human bronchi. The Ca(2+) sensitivity of human bronchial explants was also quantified on β-escin permeabilized preparations. The presence of SB203580, a p38-MAPK inhibitor, reversed the effect induced by epoxy-eicosanoid in the presence of AUDA on TNF-α-triggered Ca(2+) hypersensitivity by increasing the phosphorylation level of PKC Potentiated Inhibitor Protein-17 (CPI-17) regulatory protein. Moreover, PPARγ ligands, such as rosiglitazone and 17,18-EpETE, decreased the expression of CPI-17, both at the mRNA and protein levels, whereas this effect was countered by GW9662 treatment in TNF-α-treated bronchi. These results demonstrate that 17,18-EpETE is a potent regulator of human lung inflammation and concomitant hyperresponsiveness, and may represent a valuable asset against critical inflammatory bronchial disorder.

The aim of the present study was to investigate the anti-inflammatory effects of 14,15-epoxyeicosatrienoic acid (EET) on reactivity and Ca(2+) sensitivity in TNF-alpha-stimulated human bronchi. Tension measurements performed on either control, TNF-alpha-, or TNF-alpha + EET-pretreated bronchi revealed that 100 nM 14,15-EET pretreatments significantly reduced the reactivity of TNF-alpha-pretreated tissues to contractile agonists. EET also normalized the relaxing response to isoproterenol in TNF-alpha-treated bronchi. Pretreatment with 100 nM 14,15-EET prevented TNF-alpha-induced IkappaBalpha degradation, as demonstrated by an increase in IkappaBalpha protein levels on Western blot analysis. The anti-inflammatory properties of EET were mediated by the inhibition of IkappaBalpha degradation, suggesting a lower activation of NF-kappaB. The Ca(2+) sensitivity of TNF-alpha-stimulated bronchi was also evaluated on beta-escin-permeabilized preparations. Observed mean responses demonstrated that EET pretreatments abolished Ca(2+) hypersensitivity developed by TNF-alpha-stimulated bronchial explants. Moreover, 14,15-EET significantly reduced PDBu-induced Ca(2+) sensitivity in TNF-alpha-stimulated bronchi. Western blot and RT-PCR analyses revealed that CPI-17 protein and transcript levels were increased in TNF-alpha-treated bronchi, as opposed to being decreased in the presence of 14,15-EET. This eicosanoid also reduced U-46619-induced Ca(2+) sensitivity, which is related to the activation of Rho-kinase pathway. These results were also correlated with an increase in protein staining and transcription level of p116(Rip), a RhoA inhibitory-binding protein. Altogether, these data demonstrate that 14,15-EET is a potent modulator of the hyperreactivity triggered by TNF-alpha in human airway smooth muscle cells.

No abstract

Human cytochrome P-450 epoxygenase enzymes metabolize eicosapentaenoic acid (EPA), an omega-3-polyunsaturated fatty acid (PUFA), and leads to the production of 17(18)-epoxyeicosatetraenoic acid, or 17(18)-EpETE. The aim of the present study was to delineate the mode of action of 17(18)-EpETE on human pulmonary artery (HPA) and distal bronchi. Isometric tension measurements demonstrated that 17(18)-EpETE induced concentration-dependent relaxing effects in pulmonary artery and airway smooth muscles. Iberiotoxin (IbTx) and glyburide (Glyb), known BK(Ca) and K(ATP) channel inhibitors, respectively, reversed the relaxation induced by 17(18)-EpETE on both tissues types. Microelectrode measurements showed that exogenous addition of 17(18)-EpETE hyperpolarized the membrane potential of HPA and bronchial smooth muscle cells. These induced electrophysiological effects were reversed by the addition of 10 nM IbTx and 10 muM Glyb. Complementary experiments performed on human bronchi, using the planar lipid bilayer reconstitution technique, demonstrated that 17(18)-EpETE activated reconstituted BK(Ca) channels at low free Ca(2+) concentration. Moreover, in bronchi, the relaxing responses induced by 17(18)-EpETE were also related to reduced Ca(2+) sensitivity of the myofilaments, since free Ca(2+) concentration-response curves, performed on beta-escin-permeabilized cultured explants, were shifted toward higher Ca(2+). Together, these results provide new insight into the mode of action of 17(18)-EpETE in lung tissues and highlight this eicosanoid as a potent modulator of tone on both HPA and distal bronchi in vitro, which may be of clinical relevance in the pathophysiology of pulmonary hypertension and airway diseases.