Leukotriene C(4) enhances the contraction of porcine tracheal smooth muscle through the activation of Y-27632, a rho kinase inhibitor, sensitive pathway

Probing the biological toxicity of pyrene to the earthworm Eisenia fetida and the toxicity pathways of oxidative damage: A systematic study at the animal and molecular levels

Pyrene (Pyr), a widely used tetracyclic aromatic hydrocarbon, enters soil in large quantities and causes environmental pollution due to its production and mining. In order to systematically study the biotoxicity of pyrene to model organisms Eisenia fetida in soil, experiments were carried out from four dimensions: animal, tissue, cell and molecule. Experimental results proved that the mortality rate increased with increasing concentration and time of exposure to pyrene, while the mean body weight and spawning rate decreased. Meanwhile, when the pyrene concentration reached 900 mg/kg, the seminal vesicle and longitudinal muscle of the earthworm showed obvious atrophy. Experimental results at the cellular level showed that pyrene induced cell membrane damage and Ca²⁺ influx triggered mitochondrial membrane depolarization and a surge in ROS levels. Oxidative stress causes damage to proteins and lipids and DNA inside cells. When the mortality rate was 91.67 %, the Olive Tail Movement (OTM) of the comet experiment reached 15. The results of molecular level tests showed that pyrene inhibited the activity of Cu/Zn-superoxide dismutase (Cu/Zn-SOD) mainly by changing the microenvironment and secondary structure of amino acid Tyr 108. The weakened function of direct antioxidant enzymes may be the root cause of the excessive increase of reactive oxygen species (ROS) in cells. The systematic approach used in this study enriches the network of toxic pathways in toxicological studies, and basic data on the biological toxicity of pyrene can provide support for future soil contamination detection.

Role of Airway Smooth Muscle in Inflammation Related to Asthma and COPD

Airway smooth muscle contributes to both contractility and inflammation in the pathophysiology of asthma and COPD. Airway smooth muscle cells can change the degree of a variety of functions, including contraction, proliferation, migration, and the secretion of inflammatory mediators (phenotype plasticity). Airflow limitation, airway hyperresponsiveness, β₂-adrenergic desensitization, and airway remodeling, which are fundamental characteristic features of these diseases, are caused by phenotype changes in airway smooth muscle cells. Alterations between contractile and hyper-contractile, synthetic/proliferative phenotypes result from Ca²⁺ dynamics and Ca²⁺ sensitization. Modulation of Ca²⁺ dynamics through the large-conductance Ca²⁺-activated K⁺ channel/L-type voltage-dependent Ca²⁺ channel linkage and of Ca²⁺ sensitization through the RhoA/Rho-kinase pathway contributes not only to alterations in the contractile phenotype involved in airflow limitation, airway hyperresponsiveness, and β₂-adrenergic desensitization but also to alteration of the synthetic/proliferative phenotype involved in airway remodeling. These Ca²⁺ signal pathways are also associated with synergistic effects due to allosteric modulation between β₂-adrenergic agonists and muscarinic antagonists. Therefore, airway smooth muscle may be a target tissue in the therapy for these diseases. Moreover, the phenotype changing in airway smooth muscle cells with focuses on Ca²⁺ signaling may provide novel strategies for research and development of effective remedies against both bronchoconstriction and inflammation.

Integrated Network Analysis Reveals an Association between Plasma Mannose Levels and Insulin Resistance

To investigate the biological processes that are altered in obese subjects, we generated cell-specific integrated networks (INs) by merging genome-scale metabolic, transcriptional regulatory and protein-protein interaction networks. We performed genome-wide transcriptomics analysis to determine the global gene expression changes in the liver and three adipose tissues from obese subjects undergoing bariatric surgery and integrated these data into the cell-specific INs. We found dysregulations in mannose metabolism in obese subjects and validated our predictions by detecting mannose levels in the plasma of the lean and obese subjects. We observed significant correlations between plasma mannose levels, BMI, and insulin resistance (IR). We also measured plasma mannose levels of the subjects in two additional different cohorts and observed that an increased plasma mannose level was associated with IR and insulin secretion. We finally identified mannose as one of the best plasma metabolites in explaining the variance in obesity-independent IR.

The importance of complete tissue homogenization for accurate stoichiometric measurement of myosin light chain phosphorylation in airway smooth muscle

The standard method for measuring the phosphorylation of the regulatory myosin light chain (MLC20) in smooth muscle is extraction of the light chain using a urea extraction buffer, urea-glycerol gel electrophoresis of the soluble portion of the extract (supernatant) and Western blot analysis. The undissolved portion of the tissue during extraction (the pellet) is usually discarded. Because the pellet contains a finite amount of MLC20, omission of the pellet could result in inaccurate measurement of MLC20 phosphorylation. In this study we compared the level of tracheal smooth muscle MLC20 phosphorylation in the supernatant alone, with that in the complete tissue homogenate (supernatant and pellet) using the standard method. The supernatant fraction showed the well-known double bands representing phosphorylated and un-phosphorylated MLC20. The dissolved pellet fraction showed varying amounts of un-phosphorylated and phosphorylated MLC20. There was a small but statistically significant overestimation of the percent MLC20 phosphorylation if the pellet was not taken into consideration. The overestimation was 7% ± 2% (mean ± SEM) (p < 0.05) in unstimulated muscle and 2% ± 1% (p < 0.05) in acetylcholine (10(-6) mol/L) stimulated muscle. This finding suggests that for accurate estimation of the stoichiometry of MLC20 phosphorylation it is necessary to consider the contribution from the pellet portion of the muscle tissue homogenate.

Asthmatic airway hyperresponsiveness: the ants in the tree

Airways from asthmatics have a propensity to narrow excessively in response to spasmogens (i.e., contractile agonists), a feature called airway hyperresponsiveness (AHR). AHR is an important contributor to asthma symptoms because the degree of responsiveness dictates the amount of airway narrowing that occurs in response to inflammation-derived spasmogens produced endogenously following exposure to environmental triggers, such as allergens, viruses, or pollutants. The smooth muscle encircling the airways is responsible for responsiveness because it constricts the airway lumen when commanded to contract by spasmogens. However, whether AHR seen in asthmatics is due to stronger muscle is equivocal. In this opinion article, I propose that environmental triggers and other inflammatory molecules released during asthma attacks contribute to AHR by increasing muscle force.

High glucose enhances responsiveness of human airways smooth muscle via the Rho/ROCK pathway

Glucose moves into airway secretions after a glucose load. Therefore people with diabetes or hyperglycemia spend a significant proportion of each day with glucose in their airways secretions. This study investigated the effects of glucose on isolated human airways and on cultured airway smooth muscle (ASM) cells. Human isolated bronchi were stimulated with acetylcholine, histamine, and transmural stimulation and treated with the selective ROCK inhibitors Y27632 and SB772077B under high-glucose conditions. The effect of high glucose concentrations on intracellular calcium flux and the phosphorylation of MYPT1 in ASM cells was also investigated. High (44 mM for 6 h) glucose, but not mannitol, concentrations led to an enhanced responsiveness of ASM to contractile agents. Y27632 and SB772077B completely abolished (P < 0.05) the enhanced contractile effects with a high-concentration glucose solution, compared with control tissues. In cultured ASM cells, incubation with high glucose concentrations significantly (P < 0.05) enhanced bradykinin-induced intracellular calcium flux and the levels of pMYPT1, which were inhibited by Y27632 (P < 0.05). Our study has demonstrated that high glucose concentrations leads to hyperresponsiveness of human isolated bronchi and enhances intracellular calcium release in cultured ASM cells via a Rho/ROCK- and pMYPT1-dependent pathway, suggesting that this crucial pathway may contribute to the reduced lung function observed in patients with diabetes. These data propose novel targets for the treatment of patients with respiratory diseases that also suffer from diabetes mellitus.

Strategy for NSAID administration to aspirin-intolerant asthmatics in combination with PGE2 analogue: a theoretical approach

Aspirin-induced asthma (AIA) is a severe inflammatory disease, which affects aspirin-intolerant patients after ingestion of aspirin or other non-steroidal anti-inflammatory drugs (NSAIDs). In this article, a mathematical model describing arachidonic acid metabolism and its interaction with NSAIDs, is used to study the strategy for safe managing of NSAIDs to AIA patients. Three different AIA patient populations are taken into consideration. First, the values of aspirin and ibuprofen limiting doses that might induce symptoms of AIA are calculated and compared to experimentally observed threshold doses to enlighten which AIA patient population is susceptible to aspirin and ibuprofen. Second, the methodology of NSAID administration is studied on AIA populations susceptible to aspirin and ibuprofen by using 1,000 mg dose of aspirin and 200 or 400 mg dose of ibuprofen followed by PGE(2) analogue dosing. Our model results show that successive doses of PGE(2) analogue applied at appropriate time after aspirin or ibuprofen ingestion would enable administration of both NSAIDs to AIA patients. PGE(2) analogue doses and the corresponding times of their applications are calculated. The model is also used to estimate the duration of symptoms of AIA for different aspirin and ibuprofen doses.

Role of expression of prostaglandin synthases 1 and 2 and leukotriene C4 synthase in aspirin-intolerant asthma: a theoretical study

Altered expressions of the key enzymes in arachidonic acid (AA) metabolism, prostaglandin synthase 1 and 2 and cysteinyl leukotriene C(4) synthase, are of importance in understanding aspirin-induced asthma. We propose a mathematical model of AA metabolism and its interaction with non-steroidal anti-inflammatory drugs (NSAIDs). Model simulations depict the impact of modified expressions of the above enzymes on the time dependent synthesis of cysteinyl leukotrienes and anti-inflammatory prostaglandins before and during NSAID exposure in different model states describing healthy humans as well as aspirin-tolerant and -intolerant asthmatics. The results are compared and evaluated with experimental data taken from the literature. Our results identify the decreased expression of prostaglandin H synthase 1 and increased expression of leukotriene C(4) synthase as the key elements in AA metabolism that contribute to increased leukotriene C(4) and decreased anti-inflammatory prostaglandins after NSAID dosing in aspirin-intolerant patients. On the other hand, the decreased expression of prostaglandin H synthase 2 implies permanently increased leukotriene C(4) and lowers the sensitivity to increased drug doses. The model is used for identification of susceptible patient populations for aspirin and ibuprofen, and for identification of critical aspirin doses that might induce bronchoconstriction.

A Rho-kinase inhibitor, Y-27632, reduces cholinergic contraction but not neurotransmitter release

This study examined the effects of the selective Rho-kinase inhibitor Y-27632 [(+)-(R)-trans-4-(1-aminoethyl)-(4-pyridyl)cyclohexanecarboxamide dihydrochloride]) on cholinergic nerve-mediated contraction and neurotransmitter release in murine and guinea-pig isolated tracheal preparations. In tracheal preparations obtained from both species, Y-27632 shifted carbachol concentration-effect curves to the right and reduced the maximal contractile response. Repeated electrical field stimulation (EFS) evoked transient, consistent and reproducible contractions in murine and guinea-pig tracheal preparations. Y-27632 inhibited these cholinergic nerve-mediated contractions in a concentration-dependent manner. EFS (0.1-30 Hz) elicited frequency-dependent cholinergic nerve-mediated contractile responses. In murine tracheal preparations, Y-27632 (3 microM and 10 microM) shifted frequency-response curves to EFS to the right by 5.5 and 13.0 fold respectively and markedly reduced the maximal contractile response. In murine and guinea-pig tracheal preparations loaded with [(3)H]-choline, Y-27632 (10 microM) significantly increased the EFS-induced outflow of radioactivity from airway cholinergic nerves by 27% and 54% respectively. Thus, Y-27632 inhibited both carbachol-induced and cholinergic nerve-mediated contractile responses. Conversely, Y-27632 increased neurotransmitter release from airway cholinergic nerves. However, since antagonism of acetylcholine-induced contraction by Y-27632 overwhelmed the increased neurotransmitter release, the overall effect of this Rho-kinase inhibitor was to inhibit cholinergic nerve-mediated contraction.

Rho kinase, myosin-II, and p42/44 MAPK control extracellular matrix-mediated apical bile canalicular lumen morphogenesis in HepG2 cells

The molecular mechanisms that regulate multicellular architecture and the development of extended apical bile canalicular lumens in hepatocytes are poorly understood. Here, we show that hepatic HepG2 cells cultured on glass coverslips first develop intercellular apical lumens typically formed by a pair of cells. Prolonged cell culture results in extensive organizational changes, including cell clustering, multilayering, and apical lumen morphogenesis. The latter includes the development of large acinar structures and subsequent elongated canalicular lumens that span multiple cells. These morphological changes closely resemble the early organizational pattern during development, regeneration, and neoplasia of the liver and are rapidly induced when cells are cultured on predeposited extracellular matrix (ECM). Inhibition of Rho kinase or its target myosin-II ATPase in cells cultured on glass coverslips mimics the morphogenic response to ECM. Consistently, stimulation of Rho kinase and subsequent myosin-II ATPase activity by lipoxygenase-controlled eicosatetranoic acid metabolism inhibits ECM-mediated cell multilayering and apical lumen morphogenesis but not initial apical lumen formation. Furthermore, apical lumen remodeling but not cell multilayering requires basal p42/44 MAPK activity. Together, the data suggest a role for hepatocyte-derived ECM in the spatial organization of hepatocytes and apical lumen morphogenesis and identify Rho kinase, myosin-II, and MAPK as potentially important players in different aspects of bile canalicular lumen morphogenesis.

Inhibition of Rho-kinase normalizes nonspecific hyperresponsiveness in passively sensitized airway smooth muscle preparations

Currently, little is known about mechanisms underlying passive sensitization-induced nonspecific airway hyperresponsiveness. We sought to determine whether the nonspecific airway hyperresponsiveness observed after passive sensitization involves an increased role of Rho-kinase in airway smooth muscle contraction. In addition, the contribution of Rho-kinase to specific allergen-induced airway smooth muscle contraction was studied. Guinea pig tracheal smooth muscle preparations were incubated for 16 h, in the presence of serum obtained from nonsensitized guinea pigs or atopic serum obtained from actively ovalbumin-sensitized guinea pigs. After incubation, the contribution of Rho-kinase to histamine-, methacholine- or ovalbumin-induced isometric contractions was determined, using the specific Rho-kinase inhibitor Y-27632. Maximal contractions induced by histamine and methacholine were significantly increased in passively sensitized preparations, without a change in potency (-logEC50). In control preparations, Y-27632 reduced the potency of both agonists, without affecting maximal contraction. Remarkably, the increased agonist responsiveness induced by passive sensitization was fully normalized by Y-27632. Treatment with Y-27632 also reduced ovalbumin-induced contraction in these preparations. This study shows that the nonspecific airway smooth muscle hyperresponsiveness as well as the specific allergen responsiveness induced by passive sensitization are dependent on Rho-kinase. The complete inhibition by Y-27632 of the passive sensitization-induced increased responsiveness toward histamine and methacholine indicates a pivotal role of Rho-kinase in this process.

Allergic sensitization enhances the contribution of Rho-kinase to airway smooth muscle contraction

1. Repeated allergen challenge has been shown to increase the role of Rho-kinase in airway smooth muscle (ASM) contraction. We considered the possibility that active allergic sensitization by itself, that is, without subsequent allergen exposure, could be sufficient to enhance Rho-kinase-mediated ASM contraction. 2. Guinea pigs were actively IgE-sensitized to ovalbumin (OA), using Al(OH)(3) as adjuvant. Contractile responsiveness to G(q)-coupled receptor agonists (methacholine, histamine or PGF(2alpha)) was investigated in tracheal rings. No effect of sensitization was observed on basal- and methacholine-induced myogenic tone. In contrast, potency of histamine and PGF(2alpha) increased, that is, EC(50) decreased, after OA-sensitization by 2.6- and 4.7-fold, respectively, without effect on maximal contraction (E(max)). 3. Basal tone in preparations from both control and OA-sensitized animals was strongly decreased in the presence of the Rho-kinase inhibitor (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide (Y-27632) (1 microm). In control preparations, the E(max) and potency of histamine were unaffected by Y-27632, but were decreased for PGF(2alpha) (by 38.2% and 2.0-fold, respectively). However, in preparations from OA-sensitized animals, Y-27632 induced a significant reduction in E(max) (33.5%) and potency (2.3-fold) of histamine and of PGF(2alpha) (48.3% and 6.6-fold, respectively), normalizing the OA-sensitization-induced increase in sensitivity toward these agonists. 4. We also investigated the contribution of Rho-kinase in vivo by measuring airway responsiveness toward inhaled histamine in permanently instrumented, unanaesthetized control and OA-sensitized guinea pigs. Treatment with Y-27632 by inhalation (5 mm, nebulizer concentration) decreased airway responsiveness toward histamine both in control and OA-sensitized animals. However, the histamine PC(100) ratio pre/post Y-27632 inhalation was significantly smaller in OA-sensitized animals as compared to control animals, indicating an enhanced contribution of Rho-kinase. 5. Expression of RhoA, an upstream activator of Rho-kinase, was significantly increased (2.6-fold) in lung homogenates of OA-sensitized guinea pigs compared to control animals, as determined by Western analysis. 6. In conclusion, the results show a receptor-dependent role of Rho-kinase in agonist-induced ASM contraction. The contribution of Rho-kinase to contractile airway responsiveness, both in vivo and ex vivo, is augmented after active allergic sensitization, as a consequence of increased expression of RhoA presumably. Inhibition of the RhoA/Rho-kinase pathway may be considered a useful pharmacotherapeutical target in allergy and asthma.

LTD4 induces hyperresponsiveness to histamine in bovine airway smooth muscle: role of SR-ATPase Ca2+ pump and tyrosine kinase

Airway hyperresponsiveness is a key feature of asthma, but its mechanisms remain poorly understood. Leukotriene D(4) (LTD(4)) is one of the few molecules capable of producing airway hyperresponsiveness. In this study, LTD(4), but not leukotriene C(4) (LTC(4)), produced a leftward displacement of the concentration-response curve to histamine in bovine airway smooth muscle strips. Neither LTC(4) nor LTD(4) modified the concentration-response curve to carbachol. In simultaneous measurements of intracellular Ca(2+) ([Ca(2+)](i)) and contraction, histamine or carbachol produced a transient Ca(2+) peak followed by a plateau, along with a contraction. LTD(4) increased the histamine-induced transient Ca(2+) peak and contraction but did not modify responses to carbachol. Enhanced responses to histamine induced by LTD(4) were not modified by staurosporine or chelerythrine but were abolished by genistein. Western blot showed that carbachol, but not histamine, caused intense phosphorylation of extracellular signal-regulated kinase 1/2 and that LTD(4) significantly enhanced the phosphorylation induced by histamine, but not by carbachol. L-type Ca(2+) channel participation in the hyperresponsiveness to histamine was discarded because LTD(4) did not modify the [Ca(2+)](i) changes induced by KCl. In tracheal myocytes, LTD(4) enhanced the transient Ca(2+) peak induced by histamine (but not by carbachol) and the sarcoplasmic reticulum (SR) Ca(2+) refilling. Genistein abolished this last LTD(4) effect. Partial blockade of the SR-ATPase Ca(2+) pump with cyclopiazonic acid reduced the Ca(2+) transient peak induced by histamine but not by carbachol. These results suggested that LTD(4) induces hyperresponsiveness to histamine through activation of the tyrosine kinase pathway and an increasing SR-ATPase Ca(2+) pump activity. L-type Ca(2+) channels seemed not to be involved in this phenomenon.

KCl evokes contraction of airway smooth muscle via activation of RhoA and Rho-kinase

Airway smooth muscle (ASM) cells express voltage-dependent Ca2+ channels, primarily of the L-subtype. These may play a role in excitation-contraction coupling of ASM, although other signaling pathways may also contribute: one of these includes Rho and its downstream effector molecule Rho-associated kinase (ROCK). Although voltage-dependent Ca2+ influx and Rho/ROCK signaling have traditionally been viewed as entirely separate pathways, recent evidence in vascular smooth muscle suggest differently. In this study, we monitored contractile activity (muscle baths) in bronchial and/or tracheal preparations from the pig, cow, and human, and further examined Rho and ROCK activities (Western blots and kinase assays) and cytosolic levels of Ca2+ (fluo 4-based fluorimetry) in porcine tracheal myocytes. KCl evoked substantial contractions that were suppressed in tracheal preparations by removal of external Ca2+ or using the selective L-type Ca2+ channel blocker nifedipine; porcine bronchial preparations were much less sensitive, and bovine bronchi were essentially unaffected by 1 microM nifedipine. Surprisingly, KCl-evoked contractions were also highly sensitive to two structurally different ROCK inhibitors: Y-27632 and HA-1077. Furthermore, the inhibitory effects of nifedipine and of the ROCK inhibitors were not additive. KCl also caused marked stimulation of Rho and ROCK activities, and both these changes were suppressed by nifedipine or by removal of external Ca2+. KCl-induced elevation of [Ca2+]i was not affected by Y-27632 but was reversed by NiCl2 or by BAPTA-AM. We conclude that KCl acts in part through stimulation of Rho and ROCK, possibly secondary to voltage-dependent Ca2+ influx.

8-Bromo-cAMP decreases the Ca2+ sensitivity of airway smooth muscle contraction through a mechanism distinct from inhibition of Rho-kinase

To clarify whether cyclic AMP (cAMP)/cAMP-dependent protein kinase (PKA) activation and Rho-kinase inhibition share a common mechanism to decrease the Ca2+ sensitivity of airway smooth muscle contraction, we examined the effects of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), a stable cAMP analog, and (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide dihydrochloride, monohydrate (Y-27632), a Rho-kinase inhibitor, on carbachol (CCh)-, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS)-, 4beta-phorbol 12,13-dibutyrate (PDBu)-, and leukotriene D4 (LTD4)-induced Ca2+ sensitization in alpha-toxin-permeabilized rabbit tracheal and human bronchial smooth muscle. In rabbit trachea, CCh-induced smooth muscle contraction was inhibited by 8-BrcAMP and Y-27632 to a similar extent. However, GTPgammaS-induced smooth muscle contraction was resistant to 8-BrcAMP. In the presence of a saturating concentration of Y-27632, PDBu-induced smooth muscle contraction was completely reversed by 8-BrcAMP. Conversely, PDBu-induced smooth muscle contraction was resistant to Y-27632. In the presence of a saturating concentration of 8-BrcAMP, GTPgammaS-induced Ca2+ sensitization was also reversed by Y-27632. The 8-BrcAMP had no effect on the ATP-triggered contraction of tracheal smooth muscle that had been treated with calyculin A in rigor solutions. The 8-BrcAMP and Y-27632 additively accelerated the relaxation rate of PDBu- and GTPgammaS-treated smooth muscle under myosin light chain kinase-inhibited conditions. In human bronchus, LTD4-induced smooth muscle contraction was inhibited by both 8-BrcAMP and Y-27632. We conclude that cAMP/PKA-induced Ca2+ desensitization contains at least two mechanisms: 1) inhibition of the muscarinic receptor signaling upstream from Rho activation and 2) cAMP/PKA's preferential reversal of PKC-mediated Ca2+ sensitization in airway smooth muscle.

Evidence for protein kinase C-mediated activation of Rho-kinase in a porcine model of coronary artery spasm

OBJECTIVE

We have recently demonstrated that protein kinase C (PKC) and Rho-kinase play important roles in coronary vasospasm in a porcine model. However, it remains to be examined whether there is an interaction between the two molecules to cause the spasm.

METHODS AND RESULTS

A segment of left porcine coronary artery was chronically treated with IL-1beta-bound microbeads in vivo. Two weeks after the operation, phorbol ester caused coronary spasm in vivo and coronary hypercontractions in vitro at the IL-1beta-treated segment; both were significantly inhibited by hydroxyfasudil, a specific Rho-kinase inhibitor. Guanosine 5'-[gamma-thio]triphosphate (GTPgammaS), which activates Rho with a resultant activation of Rho-kinase, enhanced Ca2+ sensitization of permeabilized vascular smooth muscle cells, which were resistant to the blockade of PKC by calphostin C. The GTPgammaS-induced Ca2+ sensitization was greater in the spastic segment than in the control segment. Western blot analysis revealed that only PKCdelta isoform was activated during the hypercontraction.

CONCLUSIONS

These results demonstrate that PKC and Rho-kinase coexist on the same intracellular signaling pathway, with PKC located upstream on Rho-kinase, and that among the PKC isoforms, only PKCdelta may be involved. Thus, the strategy to inhibit Rho-kinase rather than PKC may be a more specific and useful treatment for coronary spasm.

Theophylline attenuates Ca2+ sensitivity and modulates BK channels in porcine tracheal smooth muscle

Theophylline, a nonselective phosphodiesterase inhibitor, has long been regarded as a major bronchodilator in the treatment of human asthma. Using front-surface fluorometry with fura-2 and alpha-toxin permeabilization, the effects of theophylline on intracellular Ca2+ concentration ([Ca2+]i), tension development and Ca2+ sensitivity of the contractile apparatus were investigated in porcine tracheal smooth muscle strips. Application of theophylline induced a relaxation without a significant decrease in [Ca2+]i when strips were precontracted by 40 mm K+ depolarization, while theophylline significantly decreased both [Ca2+]i and tension induced by carbachol. The effects of theophylline on the increases in [Ca2+]i and tension induced by carbachol were significantly inhibited by iberiotoxin, an inhibitor of large-conductance Ca2+-activated K+ channels. In the absence of extracellular Ca2+, theophylline significantly attenuated carbachol-induced transient increases in tension development, while it did not affect carbachol-induced transient increase in [Ca2+]i. The [Ca2+]i-force relationship, which was determined by cumulative applications of extracellular Ca2+ (0-5 mm) during 40 mm K+ depolarization, was significantly shifted to the right by theophylline. In alpha-toxin permeabilized strips, theophylline significantly increased the EC50 value of [Ca2+]i for contraction and enhanced the effect of cAMP, but not of cGMP. These results indicate that theophylline induces relaxation of the porcine tracheal smooth muscle through an activation of BK channels, and a resultant decrease in [Ca2+]i and an attenuation of Ca2+ sensitivity, presumably through the action of cAMP.

Theophylline and cAMP inhibit lysophosphatidic acid-induced hyperresponsiveness of bovine tracheal smooth muscle cells

We have established an in vitro model of airway hyperresponsiveness, using a bovine tracheal smooth muscle cell (BTSMC)-embedded collagen gel lattice. When the gel was pretreated with lysophosphatidic acid (LPA), which activates the small G protein RhoA, ATP- and high K+ solution-induced gel contraction was significantly augmented. This was not due to the modulation of Ca2+ mobilizing properties, since ATP- and high K+-induced Ca2+ transients were not significantly different between control and LPA-treated BTSMC. Y-27632, an inhibitor of Rho-kinase, suppressed the LPA-induced augmentation of gel contraction, whereas it did not inhibit the contraction of control gels. Theophylline (> or = 1 microM) reversed the LPA-induced augmentation of gel contraction, whereas it inhibited control gel contraction only with a very high concentration (100 microM). We confirmed that theophylline increased the intracellular concentration of cAMP ([cAMP]i) in BTSMC. Elevation of [cAMP]i with dibutyryl cAMP or forskolin also reversed the LPA-induced augmentation of gel contraction. Furthermore, theophylline, as well as dibutyryl cAMP and forskolin, suppressed the LPA-induced membrane translocation of RhoA, indicating that they prevented airway hyperresponsiveness by inhibiting RhoA. We conclude from these results that theophylline inhibits LPA-induced, RhoA/Rho-kinase-mediated hyperresponsiveness of tracheal smooth muscle cells due to the accumulation of cAMP.

Airway smooth muscle: new targets for asthma pharmacotherapy

Asthma, a chronic disease increasing in prevalence worldwide, is characterised by reversible airway obstruction, airway inflammation and airway smooth muscle (ASM) cell hyperplasia. The traditional view of ASM in asthma, as a regulator of bronchomotor tone, is rapidly changing. New evidence suggests that ASM cells also play an important role in the perpetuation of airway inflammation and airway remodelling. This review discusses the synthetic function of ASM cells, defined as the ability to secrete cytokines, chemokines and growth factors and express surface receptors that are important for cell adhesion and leukocyte activation. Finally, the efficacy of established asthma therapies in modifying the synthetic function of ASM cells are compared and novel targets for pharmacological intervention are discussed.

Modulation of calcium homeostasis as a mechanism for altering smooth muscle responsiveness in asthma

Airway hyperresponsiveness remains a defining characteristic of asthma. Traditional views assert that airway smooth muscle is an important structural effector cell in the bronchi that modulates bronchomotor tone induced by contractile agonists. New evidence, however, suggests that abnormalities in airway smooth muscle functions, induced by variety of extracellular stimuli, may play an important role in the development of airway hyperresponsiveness. Studies using isolated bronchial preparations or cultured cells show that inflammatory mediators and cytokines may alter calcium homeostasis in airway smooth muscle and render the cells nonspecifically hyperreactive to agonists.

Muscarinic excitation-contraction coupling mechanisms in tracheal and bronchial smooth muscles

We investigated the mechanisms underlying muscarinic excitation-contraction coupling in canine airway smooth muscle using organ bath, fura 2 fluorimetric, and patch-clamp techniques. Cyclopiazonic acid (CPA) augmented the responses to submaximal muscarinic stimulation in both tracheal (TSM) and bronchial smooth muscles (BSM), consistent with disruption of the barrier function of the sarcoplasmic reticulum. During maximal stimulation, however, CPA evoked substantial relaxation in TSM but not BSM. CPA reversal of carbachol tone persisted in the presence of tetraethylammoium or high KCl, suggesting that hyperpolarization is not involved; CPA relaxations were absent in tissues preconstricted with KCl alone or by permeabilization with beta-escin, ruling out a nonspecific effect on the contractile apparatus. Peak contractions were sensitive to inhibitors of tyrosine kinase (genistein) or Rho kinase (Y-27632). Sustained responses were dependent on Ca(2+) influx in TSM but not BSM; this influx was sensitive to Ni(2+) but not La(3+). In conclusion, there are several mechanisms underlying excitation-contraction coupling in airway smooth muscle, the relative importance of which varies depending on tissue and degree of stimulation.