Biomedical subjects

R Marthan

Publications and source records attributed to R Marthan.

At least 37 records · Page 2Linked to original sources

PubMed2000

Cellular mechanisms involved in iso-osmotic high K+ solutions-induced contraction of the estrogen-primed rat myometrium.

The aim of the present study was to investigate the mechanisms involved in the contraction evoked by iso-osmotic high K+ solutions in the estrogen-primed rat uterus. In Ca2+-containing solution, iso-osmotic addition of KCl (30, 60 or 90 mM K+) induced a rapid, phasic contraction followed by a prolonged sustained plateau (tonic component) of smaller amplitude. The KCl (60 mM)-induced contraction was unaffected by tetrodotoxin (3 microM), omega-conotoxin MVIIC (1 microM), GF 109203X (1 microM) or calphostin C (3 microM) but was markedly reduced by tissue treatment with neomycin (1 mM), mepacrine (10 microM) or U-73122 (10 microM). Nifedipine (0.01-0.1 microM) was significantly more effective as an inhibitor of the tonic component than of the phasic component. After 60 min incubation in Ca2+-free solution containing 3 mM EGTA, iso-osmotic KCl did not cause any increase in tension but potentiated contractions evoked by oxytocin (1 microM), sodium orthovanadate (160 micrM) or okadaic acid (20 microM) in these experimental conditions. In freshly dispersed myometrial cells maintained in Ca2+-containing solution and loaded with indo 1, iso-osmotic KCl (60 mM) caused a biphasic increase in the intracellular Ca2+ concentration ([Ca2+]i). In cells superfused for 60 min in Ca2+-free solution containing EGTA (1 mM), KCl did not increase [Ca2+]i. In Ca2+-containing solution, KCl (60 mM) produced a 76.0 +/- 16.2% increase in total [3H]inositol phosphates above basal levels and increased the intracellular levels of free arachidonic acid. These results suggest that, in the estrogen-primed rat uterus, iso-osmotic high K+ solutions, in addition to their well known effect on Ca2+ influx, activate other cellular processes leading to an increase in the Ca2+ sensitivity of the contractile machinery by a mechanism independent of extracellular Ca2+.

Animals↗

PubMed2000

Role of EDHF in the vasodilatory effect of loop diuretics in guinea-pig mesenteric resistance arteries.

1. Relaxing effect of loop diuretics, piretanide and furosemide in comparison with acetylcholine (ACh) was investigated in guinea-pig isolated mesenteric resistance arteries. 2. Concentration-response curves to ACh (0.001 - 10 microM) and diuretics (0.0001 - 1 microM) were constructed in noradrenaline (10 - 30 microM)-precontracted arteries incubated either in normal physiological salt solution (PSS) or in 30 mM KCl PSS (K-PSS). 3. In PSS, maximal relaxations (R(max)) and pD(2) to ACh were 87+/-2% and 7.1+/-0.1 (n=10). L-N(G)-nitro-arginine methyl ester (L-NAME, 100 microM) reduced R(max) by 20% (P<0.01, n=7) and pD(2) by 10% (P<0.01). In contrast, indomethacin (10 microM) increased R(max) by 19% (P<0.01, n=8) and pD(2) by 10% (P<0.05). Combination of L-NAME+indomethacin reversed the effect observed with either of these inhibitors used alone. In K-PSS, R(max) was attenuated by 40% (P<0.001, n=6) compared to PSS. L-NAME reduced R(max) by 65% (P<0.01, n=5) and increased pD(2) by 15 fold. L-NAME+indomethacin suppressed the resistant relaxation. 4. In PSS+L-NAME+indomethacin, inhibitors of small (SK(Ca); apamin, 0.1 microM) and large (BK(Ca); iberiotoxin and charybdotoxin, 0.1 microM) conductance Ca(2+)-sensitive K(-)-channels used alone had little effect on the ACh-response. Combination of apamin+iberiotoxin reduced R(max) by 40% (P<0.05, n=7) while apamin+charybdotoxin fully abolished the resistant relaxation. 5. In PSS, piretanide and furosemide induced relaxation with R(max): 89+/-3% vs 84+/-5% and pD(2): 8.5+/-0.1 vs 7.7+/-0.2 (P<0.01) for piretanide (n=11) and furosemide (n=10), respectively. Endothelial abrasion suppressed relaxation to diuretics. L-NAME and indomethacin used alone or in combination did not significantly modify the response to diuretics. 6. In K-PSS, piretanide-induced relaxation was abolished whereas that to furosemide was reduced by 70% (P<0.001, n=9) compared to PSS and was suppressed by L-NAME+indomethacin. In PSS+L-NAME+indomethacin, apamin slightly reduced relaxation to diuretics whereas charybdotoxin or iberiotoxin abolished the response. 7. These results indicate that ACh-evoked relaxation is mediated by both NO/PGl(2)-dependent and -independent mechanisms. The EDHF-dependent component relies on activation of Ca(2+)-activated K(+) channels, is sensitive to a combination of apamin+charybdotoxin and to a smaller degree to a combination of apamin+iberiotoxin. Loop diuretic-induced relaxation is endothelium-dependent, appears to be mediated by NO, PGl(2) and EDHF for furosemide and EDHF only for piretanide. For the two diuretics, opening of BK(Ca) channels may be involved in the relaxation.

Acetylcholine↗

PubMed2000

NO-induced modulation of calcium-oscillations in pulmonary vascular smooth muscle.

The effect of the nitric oxide (NO) donor sodium nitroprusside (SNP) on both [Ca(2+)](i)and mechanical activity was studied in the rat isolated pulmonary artery (RPA). In freshly isolated myocytes loaded with 1 microM indo-lacetoxymethyl ester for 30 min, short (40-60 s) application of ATP (100 microM) or ET-1 (0.1 microM) induced 3-6 cyclic rises in [Ca(2+)](i)(Ca-oscillations) of decreasing amplitude. Preincubation of cells with SNP (10-250 microM) for 10 min had no effect on the resting [Ca(2+)](i)value, but progressively abolished the oscillations. A similar effect was obtained with 8-bromo-cGMP (100-500 microM). SNP (0.001-100 microM) concentration-dependently relaxed ATP (10 mM, n = 4) and ET-1 (0.1 microM, n = 4)-precontracted RPA. 1H-[1,2,4]oxadiazolol [4,3,-a]quinoxalin-1-one (ODQ, 10 microM), a potent inhibitor of the cytosolic guanylyl cyclase, fully reversed the effect of SNP on ATP-induced [Ca(2+)](i)oscillations as well as on ATP-precontracted RPA. In contrast, N-[2-(methylamino)ethyl]-5-isoquinolinesulfonamide (H8, 10 microM), a potent inhibitor of cGMP-dependent protein kinase (PKG), did not alter the effect of SNP. Caffeine (5 mM) induced only one transient [Ca(2+)](i)-increase (n = 24), the amplitude of which was altered neither by SNP nor by 8-bromo-cGMP. Our results show that the relaxing effect of NO in RPA is related, at least in part, to its action on the Ca-signalling pathway. NO interacts with inositol trisphosphate pathway without interacting with the ryanodine-sensitive receptor. Finally, the effect of NO involves an increase in cGMP but appears independent of activation of PKG.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2000

Human isolated bronchial smooth muscle contains functional ryanodine/caffeine-sensitive Ca-release channels.

Human bronchial smooth muscle (HBSM) contraction is implicated in a variety of respiratory diseases, including asthma. Yet, the presence of an operative calcium-induced calcium release (CICR) mechanism, identified in various smooth muscles, has not been established in HBSM. We therefore studied Ca-releasing mechanisms in HBSM obtained at thoracotomy with special attention to ryanodine-sensitive receptor channels (RyRs). In freshly isolated bronchial myocytes, ryanodine (0.5 to 50 microM) and caffeine (1 to 25 mM) induced transient increases in the cytoplasmic calcium concentration ([Ca(2+)](i)). Higher ryanodine concentrations (> 100 microM) inhibited the caffeine-induced [Ca(2+)](i) response, which was also blocked in the presence of tetracaine (300 microM) or ruthenium red (200 microM), two potent CICR inhibitors. In HBSM strips, caffeine induced a transient contraction which, likewise, was inhibited by ryanodine and tetracaine. However, ryanodine (200 microM) modified neither the [Ca(2+)](i) response nor the contraction induced by K(+)-rich (110 mM) solution. Reverse transcriptase/polymerase chain reaction (RT-PCR) and RNase protection assay performed in HBSM have revealed the existence of mRNAs encoding only the type 3 RyR. We also characterized acetylcholine-induced [Ca(2+)](i) and contractile responses. None of these responses was altered by ryanodine or by tetracaine. These results demonstrate, for the first time, the existence of functional RyRs in HBSM cells which, owing to the type of isoform or the amount of protein expressed, are not involved, under physiologic conditions, in depolarization- or agonist-induced contraction.

Acetylcholine↗

PubMed2000

[In vitro techniques for the study of muscle contractility].

Functional studies of bronchial smooth muscle contractility, particularly in humans, are now well standardized regarding to tissues collection, tension setting and results expression. This type of model is usually considered as simple for analysis of pharmacological interactions between ligands and receptors. In fact, the multiplicity of cell types implicated in the bronchial response makes of isolated bronchi preparation a complex model. Examples are given with studies on endothelin or tachykinins. Inflammation and bronchial hyperresponsiveness models were proposed. Models of passive sensitization or pretreatment with cytokines are described. Functional studies of contractility are included in larger investigations including the analysis of the associated biochemical and electrical phenomenon.

Bradykinin↗

PubMed2000

[Special characteristics of bronchial smooth muscle cells].

Airway smooth muscle is one of the main effectors of bronchial reactivity. Our understanding of the cellular mechanisms involved in the contraction of this muscle has advanced in the recent past since isolated cells in culture can now be studied. Extracellular messengers (neurotransmitters and mediators) as well as their specific membrane receptors have been analyzed in some details. Membrane transduction of extracellular messengers brings about the formation (or the increase in the concentration) of the intracellular second messenger which, in airway smooth muscle, is cytosolic calcium (Ca2+i) via activation of calcium channels which depend on surface membrane potential changes (electromechanical coupling) on one hand and mainly via mechanisms independent of surface membrane potential changes, the so called--pharmacomechanical coupling--which involves membrane phosphoinositide metabolism. Changes in Ca2+i activate contractile proteins leading the muscle to shorten and to develop force via several controlled steps such as phosphorylation of myosin or changes in the sensitivity to Ca2+ of the contractile elements. Information about the cellular physiology and pathophysiology of this muscle is of value to design new drugs for the treatment of bronchoconstriction.

Bronchi↗

PubMed2000

[Genetic polymorphism and asthma].

Several mutations have been found in genes encoding for proteins implied in the pathophysiology or the treatment of asthma. Until now, no causal role could not be highlighted. The mutations were mainly studied on gene coding for the beta 2 adrenergic receptor being able to be associated with modifications of the phenotype of asthma or even to modifications of response to some beta 2 agonists. Certain polymorphisms of the beta 2 adrenoceptor are associated with polymorphisms in genes coding for peptides controlling the expression of the beta 2 adrenoceptors. The interpretation of the effects observed must take into account this linkage disequilibrium.

Adrenergic beta-Agonists↗

PubMed1999

Effect of chronic hypoxia on calcium signalling in airway smooth muscle cells.

Chronic hypoxia (CH) alters smooth muscle contractility. CH generally produces a sustained attenuation of vasoreactivity. In airways, this effect of CH is poorly understood although CH is frequently observed in patients with pulmonary diseases. This study was designed to examine the effect of CH on both the isometric contraction of isolated rings and the cytosolic calcium concentration ([Ca2+]i) using microspectrofluorimetry in freshly isolated cells from rat tracheal smooth muscle. Tissues were obtained from both chronically hypoxic rats maintained in a hypobaric chamber (50.5 kPa) for 15 days and normoxic animals. CH increased the sensitivity of airway smooth muscle to cholinergic agonists. This increase observed in the mechanical activity (concentration of carbachol producing 50% of the maximal force (EC50) in tissues from normoxic and hypoxic animals: 0.80 microM (0.39-1.21 microM) and 0.34 microM (0.08-0.59 microM), respectively, p<0.05) was related to an increase in the sensitivity of cholinergic-mediated Ca2+ release (acetylcholine EC50 in cells from normoxic and hypoxic animals: 0.14 microM (0.11-0.17 microM) and 0.04 microM (0.026-0.054 microM), respectively, p<0.05). It was concluded that chronic hypoxia alters calcium signalling in airway smooth muscle cells, which was associated with an increase in airway responsiveness in vitro. Whether a similar phenomenon contributes to bronchial hyperresponsiveness in chronically hypoxaemic patients remains to be established.

Acetylcholine↗

PubMed1999

Mast cell tryptase as a mediator of hyperresponsiveness in human isolated bronchi.

BACKGROUND: Although the role of mediators and cytokines produced by mast cells is well established in asthmatic bronchial inflammation, the contribution of mast cell-derived proteases to the development of hyperresponsiveness remains unclear. There have been reports indicating that tryptase alters the mechanical activity of animal airway smooth muscle or spontaneously sensitized human isolated airways. OBJECTIVE: The aim of this study was to analyse the effect of purified mast cell tryptase on non-sensitized human isolated bronchi. METHODS: Both central and peripheral bronchi, dissected from lung specimens obtained at thoracotomy, were studied in terms of both mechanical activity i.e. isometric contraction in response to a variety of agonists and distribution of inflammatory cells i.e. immunohistochemistry. RESULTS: In both proximal and distal bronchi, the reactivity to histamine was significantly increased by a previous incubation in the presence of 1 microg/mL of tryptase (increase in maximal force, DeltaFmax was 12.1 +/- 3.8%, and 8.8 +/- 3.1%, respectively). This effect of tryptase on histamine-induced contraction was completely abrogated in the presence of the protease inhibitor benzamidine (100 micromol/L). Histological examination of specimens exposed to tryptase demonstrated an increase in mast cell number within the subepithelial tissue whereas mast cell numbers in the epithelial layer concomittently decreased. CONCLUSION: These results indicate that human mast cell tryptase alters the contractile response of non-sensitized human isolated bronchi and that this alteration is accompanied by a change in the mast cell distribution within the airway wall.

Bronchi↗

PubMed1999

Pregnant rat myometrial cells show heterogeneous ryanodine- and caffeine-sensitive calcium stores.

Intracellular Ca(2+) release channels such as ryanodine receptors play crucial roles in the Ca(2+)-mediated signaling that triggers excitation-contraction coupling in muscles. Although the existence and the role of these channels are well characterized in skeletal and cardiac muscles, their existence in smooth muscles, and more particularly in the myometrium, is very controversial. We have now clearly demonstrated the expression of ryanodine receptor Ca(2+) release channels in rat myometrial smooth muscle, and for the first time, intracellular Ca(2+) concentration experiments with indo 1 on single myometrial cells have revealed the existence of a functional ryanodine- and caffeine-sensitive Ca(2+) release mechanism in 30% of rat myometrial cells. RT-PCR and RNase protection assay on whole myometrial smooth muscle demonstrate the existence of all three ryr mRNAs in the myometrium: ryr3 mRNA is the predominant subtype, with much lower levels of expression for ryr1 and ryr2 mRNAs, suggesting that the ryanodine Ca(2+) release mechanism in rat myometrium is largely encoded by ryr3. Moreover, using intracellular Ca(2+) concentration measurements and RNase protection assays, we have demonstrated that the expression, the percentage of cells responding to ryanodine, and the function of these channels are not modified during pregnancy.

Animals↗

PubMed1999

Human isolated airway contraction: interaction between air pollutants and passive sensitization.

Although there is epidemiological evidence that an increase in allergic diseases such as asthma may be linked to air pollution, there is little experimental data to address this issue. The aim of this study was thus to investigate the interaction between passive sensitization and exposure to pollutants in human isolated airways. We have examined (1) the effect of a preexposure to pollutants on the contraction of sensitized bronchi to a specific antigen, and (2) the effect of passive sensitization on the contraction to nonspecific agonists in bronchi preexposed to pollutants. In tissues sensitized by incubation in sera from asthmatic patients, preexposure to 0.3 microM acrolein (an aldehyde) for 10 min or 20 min significantly increased the maximal contractile response to the antigen Dermatophagoides pteronyssinus (D. pter.) by 20.5 +/- 6.5 and 34.9 +/- 7.4%, respectively. Similarly, preexposure to ozone (1 ppm for 20 min) increased the response to D. pter. by 25.3 +/- 11.3%. On the other hand, passive sensitization increased the contractile response to carbachol or histamine of bronchial rings preexposed to 0.3 microM acrolein for 10 min by 33.5 +/- 6.2% and 32.5 +/- 5.1%, respectively. This study provides a proof of principle in vitro for a combined effect of immunological sensitization and exposure to pollutants, i.e., passive sensitization and exposure to pollutants act in a synergistic manner on human bronchial smooth muscle reactivity in response to both specific antigen and nonspecific agonists.

Acrolein↗

PubMed1999

Assessment of bronchial inflammation using an automated cell recognition system based on colour analysis.

The aim of this study was to develop an automated system of cell recognition based upon colour analysis suitable for microscopic examination of bronchial inflammation. Human bronchi obtained from 17 patients undergoing thoracotomy were embedded in glycolmethacrylate to perform immunohistochemistry with antibodies against: neutrophil elastase, tryptase, chymase, eosinophil cationic protein, CD68, CD3 and immunoglobulin E. The image analysis system calculates three independent criteria (optic density, hue density, hue) combined with morphological parameters to specifically recognize a positive staining. This automated analysis was applied to the study of bronchial inflammation in smokers and nonsmokers in terms of the absolute number of cells and the expression of different markers by a single cell. The use of these criteria enabled the characterization of a positive stain on single (intraclass correlation coefficient (ICC) = 0.88 or serial (ICC = 0.84) sections. Cell counts obtained by the automated system were highly reproducible. Regarding bronchial inflammation, it was found that the number of inflammatory cells was significantly higher in smokers than in nonsmokers, the majority of these cells bearing immunoglobulin E. These results demonstrate that such computerized analysis of colours is a valuable method for quantifying inflammatory cells in bronchial tissue and for analysing the expression of different markers by a single cell.

Aged↗

PubMed1999

Pneumothoraces and chest tube placement after CT-guided transthoracic lung biopsy using a coaxial technique: incidence and risk factors.

OBJECTIVE: This study investigates factors influencing the risk of pneumothorax and chest tube placement in patients undergoing CT-guided transthoracic lung biopsy for pulmonary lesions using a coaxial technique. SUBJECTS AND METHODS: The study included 307 patients with pulmonary lesions biopsied under CT guidance. Patient-related parameters considered were age, sex, presence of emphysema or bullae, and lung function data. Lesion-related variables were size, location, cavitary appearance on CT, pleural contact, and depth of the lesion. Procedure variables were duration, type of needle, and experience of the operator. All variables were analyzed as single and multiple dependent variables for occurrence of pneumothorax. RESULTS: Pneumothorax occurred in 61 (19.9%) of the 307 patients, and chest tube placement was required in six patients (2.0%). Univariate analysis showed that lesion size, lesion location, lesion depth, and difficulty of the procedure were significantly associated with a higher rate of pneumothorax. Using multivariate logistic regression analysis, we found that lesion depth from the pleural entry point was the sole variable that was significantly associated with an increased risk of pneumothorax. This risk increased with the depth of the lesion. Chest tube placement was required more frequently in patients with severe emphysema, obstructive lung disease, or hyperinflation. CONCLUSION: Lesion depth is the predominant risk factor for pneumothorax in patients undergoing CT-guided transthoracic lung biopsy. Chest tube placement is necessary more frequently in patients with severe emphysema, obstructive lung disease, or hyperinflation.

Adult↗

PubMed1999

[Cellular pathophysiologic effects of various air pollutants on the airways].

Both epidemiological and experimental data indicate that major health consequences of urban air pollution i.e., respiratory symptoms are related, at least in part, to an alteration in the cellular processes implicated in bronchial responsiveness. In the Laboratory, we have set up techniques which enable to pre-expose in vitro human isolated bronchi to some air pollutants. Using these techniques, we have examined the dosimetric relationships and the cellular mechanisms of bronchial responsiveness altered by nitrogen dioxide (NO2), ozone (O3) or aldehydes such as acrolein. The combined effects of gas pollutants and passive immunological sensitization on bronchial hyperresponsiveness have also been studied. As a general rule, experimental protocols consisted in a comparison of the responsiveness of human bronchial tissues (obtained at thoracotomy from patients undergoing resection for pulmonary carcinoma) following ex vivo exposure to air pollutants with that of paired tissues unexposed to pollutants which acted as temporal controls. We have observed that the responsiveness of human isolated bronchi is increased following pre-exposure to NO2 or O3 or to acrolein for 15 to 30 min, at concentrations in the range of ppm and microM, respectively. A common target for the action of these pollutants on airway smooth muscle reactivity has been identified i.e., the release of intracellular stored calcium ions. Direct measurements of cytosolic calcium concentration in isolated airway smooth muscle cells exposed to pollutants have confirmed this hypothesis. Finally, we have obtained results indicating that passive sensitization and exposure to pollutants act in a additional manner on human bronchial smooth muscle reactivity in response to both specific antigen and non specific agonists. Collectively, these experimental in vitro results enable (i) to establish dosimetric relationships, (ii) to examine the cellular mechanisms and (iii) to identify populations at risk for various gas pollutants.

Air Pollutants↗

PubMed1998

Muscarinic stimulation of airway smooth muscle cells.

1. Acetylcholine, the principal neurotransmitter of the parasympathetic nervous system, is released at both ganglionic synapses and postganglionic neuroeffector junctions and acts by activation of nicotinic and muscarinic cholinoceptors. This review focuses on the effects of postjunctional muscarinic stimulation of airway smooth muscle. 2. On pharmacological criteria, four distinct subtypes of muscarinic cholinoceptor, denoted M1, M2, M3 and M4 receptors, have been identified by use of selective antagonists. Cloned muscarinic cholinoceptors are members of the family of GTP-binding protein-coupled receptors, which are characterized by seven transmembrane (TM) regions connected by intra- and extracellular loops. Between the fifth and the sixth TM regions, muscarinic receptors possess a large intracytoplasmic loop that is considered to be responsible for G-protein-coupling selectivity and exhibits high divergence between the different subtypes. 3. At the site of the smooth muscle itself, both binding and Northern blot studies have demonstrated, in a variety of species, that muscarinic receptor subtypes present are M2 and M3. M2 receptors are coupled to Gi proteins and adenylyl cyclase inhibition and thus to cAMP signaling. M3 receptors are coupled to Gq/11 protein and phosphoinositide hydrolysis and thus to calcium signaling. 4. Muscarinic-induced contraction of airway smooth muscle is mediated by M3 receptors. M2-mediated inhibition of adenylyl cyclase contributes to the prevention of bronchodilation. Cross-talk between muscarinic and beta2 adrenoceptors is likely to be present in airway smooth muscle. The pathophysiological role of this cross-talk requires further investigation.

Cholinergic Agents↗

PubMed1998

Effects of intravenous anesthetics on normal and passively sensitized human isolated airway smooth muscle.

BACKGROUND: General anesthetics may modify airway responsiveness. The authors investigated the effect of thiopental, propofol, and etomidate on airway smooth muscle. METHODS: Contraction experiments were done in human airway rings that were either normal or passively sensitized with asthmatic serum. The effect of propofol and etomidate was also studied on both [Ca2+]i increase measured by microspectrofluorimetry in isolated myocytes and isometric contraction in the rat trachea. RESULTS: In human bronchi, thiopental (10[-7] to 10[-4] M) induced a concentration-dependent contraction. Neither propofol nor etomidate altered baseline tone, but both anesthetics reduced histamine-induced contraction. In human immunologically sensitized isolated bronchi, propofol (3 x 10[-4] M) reduced histamine reactivity (deltaFmax in %) to a greater degree than in nonsensitized tissues (64.4 +/- 15.7% and 16.4 +/- 8.5%, respectively; n = 6, P < 0.05), whereas the effect of etomidate (10[-4] M) was similar in both types of tissue (24.1 +/- 6% and 22.3 +/- 15%, respectively, n = 6). In rat isolated tracheal myocytes, propofol (3 x 10[-4] M) and etomidate (10[-4] M) altered the [Ca2+]i signal in response to the depolarizing agent potassium chloride and the muscarinic agonist acetylcholine. Accordingly, the two anesthetics also reduced the mechanical response of rat tracheal rings to these agonists. CONCLUSIONS: Whereas thiopental contracts human isolated bronchi, propofol and etomidate reduce histamine-induced contraction in human isolated airway smooth muscle that were either not sensitized or passively sensitized with asthmatic serum. This effect involves inhibition of both electro- and pharmacomechanical coupling.

Anesthetics, Intravenous↗

PubMed1998

Cellular mechanisms and role of endothelin-1-induced calcium oscillations in pulmonary arterial myocytes.

The effect of endothelin (ET)-1 on both cytosolic Ca2+ concentration ([Ca2+]i) and membrane current in freshly isolated myocytes, as well as on the contraction of arterial rings, was investigated in rat main pulmonary artery (RMPA) and intrapulmonary arteries (RIPA). ET-1 (5-100 nM, 30 s) induced a first [Ca2+]i peak followed by 3-5 oscillations of decreasing amplitude. In RMPA, the ET-1-induced [Ca2+]i response was fully abolished by BQ-123 (0.1 microM). In RIPA, the response was inhibited by BQ-123 in only 21% of the cells, whereas it was abolished by BQ-788 (1 microM) in 70% of the cells. In both types of arteries, the response was not modified in the presence of 100 microM La3+ or in the absence of external Ca2+ but disappeared after pretreatment of the cells with thapsigargin (1 microM) or neomycin (0.1 microM). In RPMA myocytes clamped at -60 mV, ET-1 induced an oscillatory inward current, the reversal potential of which was close to the equilibrium potential for Cl-. This current was unaltered by the removal of external Ca2+ but was abolished by niflumic acid (50 microM). In arterial rings, the ET-1 (100 nM)-induced contraction was decreased by 35% in the presence of either niflumic acid (50 microM) or nifedipine (1 microM). These results demonstrate that ET-1 via the ETA receptor only in RMPA and both ETA and ETB receptors in RIPA induce [Ca2+]i oscillations due to iterative Ca2+ release from an inositol trisphosphate-sensitive Ca2+ store. Ca2+ release secondarily activates an oscillatory membrane Cl- current that can depolarize the cell membrane, leading to an influx of Ca2+, this latter contributing to the ET-1-induced vasoconstrictor effect.

Animals↗

PubMed1998

Immunoglobulin E-induced passive sensitization of human airways: an immunohistochemical study.

In vivo, IgE production is related to bronchial hyperresponsiveness and, in vitro, passive sensitization of human airways with asthmatic serum containing a high concentration of IgE enhances the contractile response to a variety of agonists. However, cell types implicated in this IgE sensitization are not fully determined. The aim of this study was to determine IgE-bearing cells during passive sensitization with special reference to mast cells. Peripheral bronchi were dissected out from 10 lung specimens obtained at thoracotomy and processed into glycolmethacrylate resin. Sections, each 2 microm thick, were passively sensitized by incubation for 2 h at 37 degrees C in either buffer supplemented with monoclonal IgE or asthmatic serum with a high concentration of IgE (> or = 1,000 IU/ml). Immunohistochemistry was performed using monoclonal antibodies directed against the epsilon chain, and markers of the various IgE-bearing cells (e.g., AA1, antichymase). The number of IgE-bearing cells was significantly higher in passively sensitized specimens as compared with nonsensitized specimens (6.63 +/- 1.71 versus 4.29 +/- 1.35/mm2; p = 0.013, n = 10). Mast cells represented 65% of IgE-bearing cells, 41.6 and 23.4% for TC and T subtypes, respectively. These results indicate that mast cell is the main cell type involved in IgE-induced passive sensitization. The involvement of mast cell-derived tryptase in the mechanisms of IgE-related hyperresponsiveness should be further examined.

Adult↗