Electromechanical effects of endothelin on ferret bronchial and tracheal smooth muscle

Effects of histamine and endothelin-1 on membrane potentials and ion currents in bovine tracheal smooth-muscle cells

We tested the effects of tetraethylammonium (TEA), acetylcholine (ACh), histamine, and endothelin-1 on single airway smooth-muscle cells from bovine trachea, using the patch-clamp technique. Resting membrane potential was -48 +/- 1 mV (n = 47). Both TEA and ACh significantly depolarized the membrane, by +28 +/- 4 mV (P < 0.001, n = 12) and +21 +/- 2 mV (P < 0.01, n = 7), respectively, in the whole-cell configuration. In contrast, both histamine and endothelin-1 hyperpolarized the membrane, by -21 +/- 6 mV (P < 0.01, n = 8) and -15 +/- 2 mV (P < 0.01, n = 8), respectively. Calcium-dependent large-conductance K+-channels (127 pS) and small-conductance K+ channels (21 pS) were identified in excised patches. The small-conductance K+ channel was inhibited by 4-aminopyridine and activated by both histamine and endothelin-1. Furthermore, TEA did not alter the membrane hyperpolarization by these agonists, suggesting that the small-conductance K+ channel or delayed-rectifier K+ channel was involved in the membrane hyperpolarization. Membrane hyperpolarization by histamine and endothelin-1 suggests that activation of voltage-dependent calcium channels (VDCCs) or of calcium influx does not contribute substantially to the contractile response of airway smooth-muscle contraction to these agonists.

Prostanoids counterbalance the bronchoconstrictor activity of endothelin-1 in pigs

In 12 anaesthetized spontaneously breathing pigs divided into two groups of six animals we evaluated the respiratory and haemodynamic responses to endothelin-1 (ET-1) administered by aerosol (200 pmol x kg(-1) in 1 ml of saline solution). In the first group (control group), the responses to ET-1 were evaluated before and after the blocking of endogenous nitric oxide (NO) by NG-nitro-L-arginine methyl ester (L-NAME 5 mg x kg(-1), i.v.). In the second group (indomethacin-pretreated group), the experimental protocol was similar to that of the control group, but the responses were evaluated after the blocking of endogenous prostanoids by indomethacin (3 mg x kg(-1), i.v.). Results show that in the control group ET-1 administered before and after L-NAME did not change compliance (Crs) or resistances (Rrs) of the respiratory system. In indomethacin-pretreated pigs, ET-1 significantly increased Rrs and decreased Crs. This constrictor effect appearing only during the block of arachidonic acid metabolites showed that ET-1 activity can be counterbalanced by a release of dilator prostanoids. In this group after L-NAME pretreatment ET-1 did not alter the mechanical properties of the respiratory system, suggesting an involvement of other bronchodilator mechanisms. In the control group, aerosol administered ET-1 increased mean systemic (MAP) and pulmonary (MPAP) arterial pressures, while when ET-1 was administered after L-NAME pretreatment, MPAP decreased. In the indomethacin-pretreated group, the peptide did not modify MAP, but caused an early decrease in MPAP when administered after L-NAME. Therefore, our results show that ET-1 caused a bronchoconstrictor effect only in indomethacin-pretreated pigs and suggest that the intrinsic constrictor activity of the peptide can be modulated especially by the release of dilator prostanoids.

Expression and function of endothelins, endothelin receptors, and endothelin converting enzyme in the porcine trachea

Endothelins (ETs) can modulate the airway smooth muscle tone. Using simultaneous measurements of cytosolic Ca2+ concentration ([Ca2+]i) and tension as well as the reverse transcription polymerase chain reaction (RT-PCR), we examined ET systems in the porcine trachea. In the functional study, the application of ET-1, ET-3 or sarafotoxin S6c (S6c) caused increases in [Ca2+]i and tension, in a concentration-dependent manner. These ET ligands were found to increase the Ca2+ sensitivity of the myofilament of the tracheal smooth muscle cells (SMCs). The contractions induced by ET-1 (10(-7) M), an ET receptor (ET-R) non-selective agonist, were much greater than those induced by S6c, an ET(B)-R selective agonist. BQ-123 (10(-6) M), an ET(A)-R antagonist, inhibited the ET-1 induced contraction. These functional experiments suggested the presence of both functioning ET(A)- and ET(B)-Rs in tracheal SMCs. RT-PCR experiments revealed that the tracheal SMCs expressed both ET(A)-R and ET(B)-R mRNAs, while tracheal epithelial cells (EpCs) predominantly expressed ET(A)-R mRNA. The porcine tracheal SMCs and EpCs also expressed pre-pro ET-1 (ppET-1), ppET-3, and endothelin converting enzyme-1 (ECE-1) mRNAs. These results suggested that ETs induce contraction of porcine tracheal SMCs not only by increasing [Ca2+]i but also increasing the Ca2+ sensitivity of the myofilament and that ETs could potentially be the autocrine and/or paracrine transmitters to regulate the contraction in the porcine airway smooth muscle.

Different modes of endothelin-1 action in pressor response in vivo and pulmonary parenchymal contraction in vitro in the guinea pig

Intravenously administered endothelin-1 (ET-1) (2 x 10(-11)-6 x 10(-10) mol/kg) induced dose-dependent pressor responses in anesthetized guinea pigs. Pretreatment with indomethacin (5 mg/kg, i.v.) or with a thromboxane A2/prostaglandin endoperoxide receptor antagonist, ONO-3708 (0.5 and 1.0 mg/kg, i.v.) significantly attenuated the pressor responses. ET-1 (10(-11)-10(-7) M) dose-dependently contracted guinea pig pulmonary parenchymal strips in vitro. However, neither pretreatment with indomethacin (10(-5) M) nor one with ONO-3708 (10(-6) M and 10(-5) M) significantly affected the ET-1-induced guinea pig pulmonary parenchymal contraction in vitro. Moreover, pretreatment with a platelet activating factor receptor antagonist, CV-3988 (2 x 10(-5) M) did not significantly affect the contraction. Thus, in guinea pigs, the mechanism of ET-1-induced pressor response in vivo mediated via cyclooxygenase-generated-eicosanoid(s), possibly, thromboxane A2 is not identical to that of ET-1-induced contraction of pulmonary parenchymal strips in vitro.

Endothelin-induced contraction and mediator release in human bronchus

1. To elucidate the role of acetylcholine and various autacoids in endothelin-1 (ET-1)-induced contraction in human bronchus, the effects of various receptor antagonists were examined. In addition, the ability of ET-1 to stimulate the release of histamine, peptidoleukotrienes and prostanoids was determined. 2. ET-1 was a potent and effective contractile agonist in human bronchus, possessing similar potency and efficacy to leukotriene D4 (LTD4); EC50 (-log M): ET-1 = 7.76 +/- 0.09, n = 7; LTD4 = 8.46 +/- 0.53, n = 7; P > 0.2; maximum response (% 10 microM pre-carbachol): ET-1 = 103.8 +/- 17.4, n = 7; LTD4 = 95.5 +/- 9.3, n = 7; P > 0.6. 3. The cyclo-oxygenase inhibitor, sodium meclofenamate (1 microM) or the potent and selective thromboxane receptor antagonist, SQ 29,548 (1 microM) were without significant effect on ET-1 concentration-response curves. 4. In the presence of sodium meclofenamate (1 microM), the muscarinic receptor antagonist, atropine (1 microM), the platelet activating factor (PAF) receptor antagonist, WEB 2086 (1 microM) or the combination of the H1-histamine receptor antagonist, mepyramine (10 microM) and the leukotriene receptor antagonist, SK&F 104353 (10 microM), were without marked effect on ET-1 concentration-response curves. In addition, the combination of all four receptor antagonists did not antagonize ET-1-induced contraction. 5. ET-1 (0.3 microM) did not stimulate the release of histamine or immunoreactive leukotrienes from human bronchus. 6. ET-1 (0.3 microM) significantly stimulated the release of prostaglandin D2 (PGD2), 9alpha, 11beta PGF2 (PGD2 metabolite), PGE2, 6-keto PGF1alpha (PGI2 metabolite), PGF2alpha, and thromboxane B2 (TxB2) a lower concentration, 10 nM, was without effect on prostanoid release. The production of PGD2 was increased 7.5 fold, whereas the release of the other prostanoids was stimulated only about 1.6 to 2.7 fold.7. These data provide evidence that ET-1 elicits contraction of human isolated bronchus predominantly via a direct mechanism with no significant involvement of the release of acetylcholine, leukotrienes,histamine or PAF. Although ET-1 increased the release of several prostanoids they did not have a significant modulatory effect on the smooth muscle contraction.

Endothelin peptides: biological actions and pathophysiological significance in the lung

Endothelins (ETs) are a family of novel regulatory peptides. Besides their effects on the cardiovascular system, which have been extensively described, several lines of evidence suggest an important role for ETs in regulating pulmonary functions. ETs are present in the pulmonary tissues, bronchoalveolar space and pulmonary circulation. Release of ETs from macrophages, endothelial and epithelial cells is modulated by a variety of chemical and physical stimuli and is regulated at the level of transcription or translation. Specific endothelin receptors have been identified in the airways as well as in the pulmonary vasculature. ETs are among the most potent bronchoconstrictors yet described. In the pulmonary circulation, ETs can elicit both vasodilation and vasoconstriction and can enhance vascular permeability. ETs could also modulate activation of inflammatory cells. Enhanced ET expression and/or production have been detected in asthma, certain pulmonary tumors, shock states associated with adult respiratory distress syndrome and pulmonary hypertension. These findings suggest that by regulating pulmonary vascular and airway tone, activation of inflammatory cells and cellular growth and/or differentiation, ETs may play an important role in pulmonary pathophysiology.

Endothelin-1 inhibits pre-stimulated tracheal submucosal gland secretion and epithelial albumin transport

1. Endothelin-1 potently contracts smooth muscle, including that in the airways. However, its effect on airway mucosal function has not so far been studied. 2. We have used the ferret whole trachea in vitro to examine the effect of endothelin-1 on tracheal smooth muscle tone, transepithelial potential difference (p.d.), submucosal gland secretion (including lysozyme secretion from serous cells) and active epithelial albumin transport. In addition we have examined the effects of endothelin on submucosal gland secretion and albumin transport pre-stimulated with the muscarinic agonist methacholine and the alpha-adrenoceptor agonist phenylephrine. The effects of the Ca2+ channel blocker nifedipine on the responses to endothelin have also been assessed. 3. Endothelin (0.1-100 nM) produced concentration-dependent increases in intraluminal tracheal pressure indicating smooth muscle contraction, and in the negativity of the transepithelial p.d. These effects were partially inhibited by nifedipine (10 microM). 4. Endothelin (0.01-100 nM) had no significant effect on baseline rates of mucus, lysozyme or albumin outputs, but produced concentration-dependent reductions in maintained methacholine- and phenylephrine-induced mucus, lysozyme and albumin outputs. In general endothelin was more potent against methacholine-induced effects. All of the concentration-response curves for endothelin were shallow and some appeared to be biphasic, suggesting the possibility of more than one mechanism of action of endothelin. 5. The effects of endothelin (at concentrations greater than 1 nM) on phenylephrine-induced mucus volume, lysozyme and albumin outputs were significantly inhibited by nifedipine. Similarly the effect of endothelin (greater than 1 nM) on methacholine-induced mucus volume and albumin outputs (but not lysozyme output) was attenuated by nifedipine. Similarly the effect of endothelin (>1 nM) on methacholine-induced mucus volume and albumin outputs (but not lysozyme output) was attenuated by nifedipine. The effects of endothelin (at concentrations <1 nM) on methacholine and phenylephrine-induced responses were generally not affected by nifedipine.6. Thus, endothelin contracts ferret tracheal smooth muscle and increases transepithelial p.d. at least in part by opening dihydropyridine-sensitive Ca2+ channels. Endothelin does not directly stimulate submucosal gland secretion or epithelial albumin transport, but inhibits methacholine- and phenylephrineinduced secretion and transport. The inhibitory effects produced by higher concentrations of endothelin may be mediated partially by activation of dihydropyridine-sensitive Ca2+ channels, although the explanation for this is not clear. The mechanism of action of endothelin in attenuating stimulated secretion and epithelial transport at lower concentrations is unknown.