Airway Smooth Muscle Contraction Research Articles

Role of dystrophin in airway smooth muscle phenotype, contraction and lung function.

Dystrophin links the transmembrane dystrophin-glycoprotein complex to the actin cytoskeleton. We have shown that dystrophin-glycoprotein complex subunits are markers for airway smooth muscle phenotype maturation and together with caveolin-1, play an important role in calcium homeostasis. We tested if dystrophin affects phenotype maturation, tracheal contraction and lung physiology. We used dystrophin deficient Golden Retriever dogs (GRMD) and mdx mice vs healthy control animals in our approach. We found significant reduction of contractile protein markers: smooth muscle myosin heavy chain (smMHC) and calponin and reduced Ca2+ response to contractile agonist in dystrophin deficient cells. Immunocytochemistry revealed reduced stress fibers and number of smMHC positive cells in dystrophin-deficient cells, when compared to control. Immunoblot analysis of Akt1, GSK3β and mTOR phosphorylation further revealed that downstream PI3K signaling, which is essential for phenotype maturation, was suppressed in dystrophin deficient cell cultures. Tracheal rings from mdx mice showed significant reduction in the isometric contraction to methacholine (MCh) when compared to genetic control BL10ScSnJ mice (wild-type). In vivo lung function studies using a small animal ventilator revealed a significant reduction in peak airway resistance induced by maximum concentrations of inhaled MCh in mdx mice, while there was no change in other lung function parameters. These data show that the lack of dystrophin is associated with a concomitant suppression of ASM cell phenotype maturation in vitro, ASM contraction ex vivo and lung function in vivo, indicating that a linkage between the DGC and the actin cytoskeleton via dystrophin is a determinant of the phenotype and functional properties of ASM.

The ROAD to a focused view of airway smooth muscle and inflammatory cells in asthmatic sensitization: a tribute to Newman Stephens.

The ROAD to a focused view of airway smooth muscle and inflammatory cells in asthmatic sensitization: a tribute to Newman Stephens.

Persistence of serotonergic enhancement of airway response in a model of childhood asthma.

The persistence of airway hyperresponsiveness (AHR) and serotonergic enhancement of airway smooth muscle (ASM) contraction induced by ozone (O3) plus allergen has not been evaluated. If this mechanism persists after a prolonged recovery, it would indicate that early-life exposure to O3 plus allergen induces functional changes predisposing allergic individuals to asthma-related symptoms throughout life, even in the absence of environmental insult. A persistent serotonergic mechanism in asthma exacerbations may offer a novel therapeutic target, widening treatment options for patients with asthma. The objective of this study was to determine if previously documented AHR and serotonin-enhanced ASM contraction in allergic monkeys exposed to O3 plus house dust mite allergen (HDMA) persist after prolonged recovery. Infant rhesus monkeys sensitized to HDMA were exposed to filtered air (FA) (n = 6) or HDMA plus O3 (n = 6) for 5 months. Monkeys were then housed in a FA environment for 30 months. At 3 years, airway responsiveness was assessed. Airway rings were then harvested, and ASM contraction was evaluated using electrical field stimulation with and without exogenous serotonin and serotonin-subtype receptor antagonists. Animals exposed to O3 plus HDMA exhibited persistent AHR. Serotonin exacerbated the ASM contraction in the exposure group but not in the FA group. Serotonin subtype receptors 2, 3, and 4 appear to drive the response. Our study shows that AHR and serotonin-dependent exacerbation of cholinergic-mediated ASM contraction induced by early-life exposure to O3 plus allergen persist for at least 2.5 years and may contribute to a persistent asthma phenotype.

Human airway smooth muscle maintain in situ cell orientation and phenotype when cultured on aligned electrospun scaffolds.

Human airway smooth muscle (HASM) contraction plays a central role in regulating airway resistance in both healthy and asthmatic bronchioles. In vitro studies that investigate the intricate mechanisms that regulate this contractile process are predominantly conducted on tissue culture plastic, a rigid, 2D geometry, unlike the 3D microenvironment smooth muscle cells are exposed to in situ. It is increasingly apparent that cellular characteristics and responses are altered between cells cultured on 2D substrates compared with 3D topographies. Electrospinning is an attractive method to produce 3D topographies for cell culturing as the fibers produced have dimensions within the nanometer range, similar to cells' natural environment. We have developed an electrospun scaffold using the nondegradable, nontoxic, polymer polyethylene terephthalate (PET) composed of uniaxially orientated nanofibers and have evaluated this topography's effect on HASM cell adhesion, alignment, and morphology. The fibers orientation provided contact guidance enabling the formation of fully aligned sheets of smooth muscle. Moreover, smooth muscle cells cultured on the scaffold present an elongated cell phenotype with altered contractile protein levels and distribution. HASM cells cultured on this scaffold responded to the bronchoconstrictor bradykinin. The platform presented provides a novel in vitro model that promotes airway smooth muscle cell development toward a more in vivo-like phenotype while providing topological cues to ensure full cell alignment.

The cell biology of asthma.

The clinical manifestations of asthma are caused by obstruction of the conducting airways of the lung. Two airway cell types are critical for asthma pathogenesis: epithelial cells and smooth muscle cells. Airway epithelial cells, which are the first line of defense against inhaled pathogens and particles, initiate airway inflammation and produce mucus, an important contributor to airway obstruction. The other main cause of airway obstruction is contraction of airway smooth muscle. Complementary experimental approaches involving cultured cells, animal models, and human clinical studies have provided many insights into diverse mechanisms that contribute to airway epithelial and smooth muscle cell pathology in this complex disease.

Testosterone-induced relaxation involves L-type and store-operated Ca2+ channels blockade, and PGE2 in guinea pig airway smooth muscle

In vascular smooth muscle, it has been described that testosterone (TES) produces relaxation by blocking L-type Ca(2+) channels. Recently, we found that L-type Ca(2+) and store-operated Ca(2+) (SOC) channels are the main membranal structures that provide extracellular Ca(2+) for carbachol (CCh)-induced contraction in airway smooth muscle (ASM). We studied the possible interactions between L-type and SOC channels in TES-induced relaxation in guinea pig ASM. TES (10, 32, 100, and 178 μM) induced a complete relaxation of CCh-precontracted tracheal smooth muscle, and indomethacin partially inhibited this response. In single myocytes, the KCl-induced intracellular Ca(2+) increase ([Ca(2+)]i) was decreased by 32 and completely blocked by 100 nM TES. This androgen (32 and 100 μM) significantly diminished (~25 and 49 %, respectively) the capacitative Ca(2+) entry. Myocytes stimulated with CCh produced a transient Ca(2+) peak followed by a sustained plateau. D-600 was added during the plateau phase, and a partial diminution (~35 %) was observed. A greater decrease (~78 %) was seen when 2-aminoethyl diphenylborinate (2-APB, SOC antagonist) was used. The combination of both drugs completely abolished the Ca(2+) plateau induced by CCh. TES (100 μM) also completely abolished the CCh-induced Ca(2+) plateau. Indomethacin significantly diminished this effect of TES. PGE2 and butaprost proportionally decreased the Ca(2+) plateau as indomethacin blocked it. Sarcoplasmic reticulum refilling was partially, dependently, and significantly diminished by TES. We concluded that TES-induced relaxation involves blockade of L-type Ca(2+) channels at nanomolar and SOC channels at micromolar concentration and PGE2 seems to be also involved in this phenomenon.

Non‐genomic relaxation effect of testosterone through L‐type and store operated Ca2+ channels blockade in guinea pig airway smooth muscle (1174.2)

In vascular smooth muscle, testosterone (TES) produces relaxation blocking L‐type Ca2+ channels. Recently, we found that L‐type and store operated (SOC) Ca2+ channels are the main membranal structures that provide extracellular Ca2+ for carbachol‐induced contraction in airway smooth muscle (ASM). Thus, we studied the possible interactions between L‐type and SOC channels in TES‐induced relaxation in guinea pig ASM. TES (10, 32 and 100 μM) induced a complete relaxation of Cch pre‐contracted tracheal smooth muscle and indomethacin partially inhibited this response. In single myocytes, the KCl induced intracellular Ca2+ increase ([Ca2+]i) was decreased by 32 and completely blocked by 100 nM TES. This androgen (32 and 100 μM) significantly diminished (~25 and 49 %, respectively) the capacitative Ca2+ entry. Myocytes stimulated with carbachol (Cch) produced a transient Ca2+ peak followed by a sustained plateau and 100 μM TES completely abolished the Cch induced Ca2+ plateau. Indomethacin, significantly diminished this effect of TES. When D‐600 was added during the plateau phase, a partial diminution (~35 %) was observed. A grater decrease (~78 %) was also seen when 2‐APB (SOC antagonist) was used. The combination of both drugs completely abolished the Ca2+ plateau induced by Cch. We concluded that TES blocks L‐type Ca2+ channels at nanomolar and SOC channels at micromolar concentration to induce relaxation.Grant Funding Source: PAPIIT‐DGAPA, UNAM IN200613

Beta adrenergic pathway independent relaxation of human airway smooth muscle (870.9)

Severe acute asthma, defined as asthma that is refractory to current anti‐inflammatory agents and bronchodilators, accounts for an estimated two‐million emergency department visits annually. β2‐adrenergic receptor (β2AR) agonists (β‐agonists) are widely used for the treatment of bronchospasm associated with acute asthma attacks, however, some patients develop refractory responses to long term usage of β –agonists. It also causes adverse effects in patients with a genetic polymorphism (Arg/Arg genotype, about a sixth of the US population) in the adrenergic receptor creating a need for additional therapeutics for managing asthma. We have shown earlier that β‐agonist induced airway smooth muscle (ASM) relaxation is associated with increases in the phosphorylation of HSP20. In this study we evaluate the effect of a transducible phosphopeptide mimetic of HSP20 protein (P20 peptide) on the relaxation of human ASM. Freshly isolated human ASM was pretreated with either a β‐agonist, isoproterenol (ISO), or the P‐20 peptide followed by a bronchoconstrictor, carbachol and force was measured in a tissue bath system. ISO blocked carbachol induced contraction in human ASM by activating the β2AR pathway. P‐20 peptide also blocked carbachol induced contraction of ASM, but in a β2AR independent manner. P20 peptide also relaxed human ASM precontracted with carbachol. These results suggest that the P20 peptide targets molecular events downstream of the β‐agonists‐cAMP pathway and that P20 peptide may be developed as a therapeutic to alleviate bronchospasm for patients who are refractory to β‐agonist, thus reducing the morbidity, mortality, and costs associated with managing asthma.Grant Funding Source: Supported by NIH RO1 70715

Development of Gs‐biased modulators of the β2‐adrenergic receptor (662.1)

Asthma is a complex disease that is manifested by enhanced airway inflammation that leads to airway smooth muscle (ASM) contraction and airway constriction. While β‐agonists serve as a major asthma therapeutic, these drugs may also increase the risk of having a severe asthmatic attack that can result in death. Since several lines of evidence suggest that β2AR interaction with β‐arrestins may play a role in these adverse effects, biased ligands that selectively promote β2AR interaction with Gs may serve as an effective way of treating asthma. While an orthosteric Gs‐biased agonist for the β2AR has yet to be identified, another strategy to stabilize the conformation of a G protein‐coupled receptor (GPCR) is to target the intracellular surface of the receptor using pepducins. Pepducins are lipidated peptides derived from the intracellular domains of a GPCR. A library of β2AR pepducins was synthesized and screened for cAMP production and β‐arrestin recruitment and identified two classes of Gs‐biased pepducins: receptor‐dependent and receptor‐independent. The Gs‐biased pepducins exhibit minimal functional desensitization in cells and do not induce GPCR kinase (GRK) phosphorylation or internalization of the β2AR, although PKA‐mediated phosphorylation was observed. The receptor‐independent pepducins appear to directly activate Gs while the receptor‐dependent pepducins promote cAMP production that is sensitive to the inverse agonist ICI 118,551, suggesting that the pepducin is stabilizing a Gs‐biased conformation of the β2AR. These pepducins represent the first reported Gs‐biased modulators and offer a potential new class of asthma therapeutics.Grant Funding Source: Supported by P01HL114471 (NHLBI) and T32GM100836 (NIGMS)

Hyperinsulinemia potentiates airway responsiveness to parasympathetic nerve stimulation in obese rats.

Obesity is a substantial risk factor for developing asthma, but the molecular mechanisms underlying this relationship are unclear. We tested the role of insulin in airway responsiveness to nerve stimulation using rats genetically prone or resistant to diet-induced obesity. Airway response to vagus nerve stimulation and airway M2 and M3 muscarinic receptor function were measured in obese-prone and -resistant rats with high or low circulating insulin. The effects of insulin on nerve-mediated human airway smooth muscle contraction and human M2 muscarinic receptor function were tested in vitro. Our data show that increased vagally mediated bronchoconstriction in obesity is associated with hyperinsulinemia and loss of inhibitory M2 muscarinic receptor function on parasympathetic nerves. Obesity did not induce airway inflammation or increase airway wall thickness. Smooth muscle contraction to acetylcholine was not increased, indicating that hyperresponsiveness is mediated at the level of airway nerves. Reducing serum insulin with streptozotocin protected neuronal M2 receptor function and prevented airway hyperresponsiveness to vagus nerve stimulation in obese rats. Replacing insulin restored dysfunction of neuronal M2 receptors and airway hyperresponsiveness to vagus nerve stimulation in streptozotocin-treated obese rats. Treatment with insulin caused loss of M2 receptor function, resulting in airway hyperresponsiveness to vagus nerve stimulation in obese-resistant rats, and inhibited human neuronal M2 receptor function in vitro. This study shows that it is not obesity per se but hyperinsulinemia accompanying obesity that potentiates vagally induced bronchoconstriction by inhibiting neuronal M2 muscarinic receptors and increasing acetylcholine release from airway parasympathetic nerves.

Extra-cellular matrix proteins induce matrix metalloproteinase-1 (MMP-1) activity and increase airway smooth muscle contraction in asthma.

Airway remodelling describes the histopathological changes leading to fixed airway obstruction in patients with asthma and includes extra-cellular matrix (ECM) deposition. Matrix metalloproteinase-1 (MMP-1) is present in remodelled airways but its relationship with ECM proteins and the resulting functional consequences are unknown. We used airway smooth muscle cells (ASM) and bronchial biopsies from control donors and patients with asthma to examine the regulation of MMP-1 by ECM in ASM cells and the effect of MMP-1 on ASM contraction. Collagen-I and tenascin-C induced MMP-1 protein expression, which for tenascin-C, was greater in asthma derived ASM cells. Tenascin-C induced MMP-1 expression was dependent on ERK1/2, JNK and p38 MAPK activation and attenuated by function blocking antibodies against the β1 and β3 integrin subunits. Tenascin-C and MMP-1 were not expressed in normal airways but co-localised in the ASM bundles and reticular basement membrane of patients with asthma. Further, ECM from asthma derived ASM cells stimulated MMP-1 expression to a greater degree than ECM from normal ASM. Bradykinin induced contraction of ASM cells seeded in 3D collagen gels was reduced by the MMP inhibitor ilomastat and by siRNA knockdown of MMP-1. In summary, the induction of MMP-1 in ASM cells by tenascin-C occurs in part via integrin mediated MAPK signalling. MMP-1 and tenascin-C are co-localised in the smooth muscle bundles of patients with asthma where this interaction may contribute to enhanced airway contraction. Our findings suggest that ECM changes in airway remodelling via MMP-1 could contribute to an environment promoting greater airway narrowing in response to broncho-constrictor stimuli and worsening asthma symptoms.

Vinculin Phosphorylation at Tyr1065 Regulates Vinculin Conformation and Tension Development in Airway Smooth Muscle Tissues

Vinculin localizes to membrane adhesion junctions in smooth muscle tissues, where its head domain binds to talin and its tail domain binds to filamentous actin, thus linking actin filaments to the extracellular matrix. Vinculin can assume a closed conformation, in which the head and tail domains bind to each other and mask the binding sites for actin and talin, and an open activated conformation that exposes the binding sites for talin and actin. Acetylcholine stimulation of tracheal smooth muscle tissues induces the recruitment of vinculin to the cell membrane and its interaction with talin and actin, which is required for active tension development. Vinculin phosphorylation at Tyr(1065) on its C terminus increases concurrently with tension development in tracheal smooth muscle tissues. In the present study, the role of vinculin phosphorylation at Tyr(1065) in regulating the conformation and function of vinculin during airway smooth muscle contraction was evaluated. Vinculin constructs with point mutations at Tyr(1065) (vinculin Y1065F and vinculin Y1065E) and vinculin conformation-sensitive FRET probes were expressed in smooth muscle tissues to determine how Tyr(1065) phosphorylation affects smooth muscle contraction and the conformation and cellular functions of vinculin. The results show that vinculin phosphorylation at tyrosine 1065 is required for normal tension generation in airway smooth muscle during contractile stimulation and that Tyr(1065) phosphorylation regulates the conformation and scaffolding activity of the vinculin molecule. We conclude that the phosphorylation of vinculin at tyrosine 1065 provides a mechanism for regulating the function of vinculin in airway smooth muscle in response to contractile stimulation.

Airway smooth muscle

Asthma is a major public health problem that afflicts nearly one in 20 people worldwide. Despite available treatments, asthma symptoms remain poorly controlled in a significant minority of asthma patients, especially those with severe disease. Accordingly, much ongoing effort has been directed at developing new therapeutic strategies; these efforts are described in detail below. Although mucus hypersecretion is an important component of asthma pathobiology, the primary mechanism of morbidity and mortality in asthma is excessive narrowing of the airway. The key end- effector of excessive airway narrowing is airway smooth muscle (ASM) contraction; overcoming ASM contraction is therefore a prominent therapeutic strategy. Here, we review exciting new advances aimed at ASM relaxation. Exciting advances in ASM biology have identified new therapeutic targets for the prevention or reversal of bronchoconstriction in asthma.

Physiology of Airway Smooth Muscle Contraction: An Overview

Bronchial reactivity is a physiological property of healthy airways to develop a moderate airway obstruction in response to various non-specific stimuli, which is altered in several pulmonary diseases. The active effector of airway reactivity is airway smooth muscle (ASM). The contractile status of airway smooth muscle is under the control of many extracellular messengers acting on specific membrane receptors. Binding of the contractile messengers to their specific membrane receptors increases cytosolic Ca2+ concentration ([Ca2+]i). The shape of the resulting calcium signal is sensed by the contractile apparatus and hence determines the pattern of the contractile response. Agonists can also modify the sensitivity of the contractile apparatus to calcium, via phosphorylation and dephosphorylation of a network of regulatory proteins. These mechanisms can be altered in several respiratory diseases such and COPD, asthma, or exposure to air pollutants, leading to hyperreactivity, which can be pharmacologically controlled by drugs acting on the mechanisms of ASM contraction. The article describes the major intracellular mechanisms responsible for the excitation-contraction coupling in airway smooth muscle cell.

Sarcoplasmic reticulum Ca2+ refilling is determined by L-type Ca2+ and store operated Ca2+ channels in guinea pig airway smooth muscle

Sarcoplasmic reticulum Ca2+ refilling (SRREF) is crucial to sustain the agonists induced airway smooth muscle contraction. Nevertheless, its mechanisms have not been clearly described yet, although L-type voltage dependent, store operated, receptor operated channels and the Na+/Ca2+ exchanger in its reverse mode (NCXREV) have been proposed as Ca2+ handling proteins participating in this process. We found that in guinea pig and bovine tracheal smooth muscle, SRREF induced by caffeine was completely abolished by thapsigargin, even in the presence of Bay K8644, an activator of the L-type Ca2+ channel. Activation of NCXREV in guinea pig tracheal myocytes increased SRREF in ~70%, while opening of the L-type Ca2+ channels with Bay K8644 and favoring the capacitative Ca2+ entry with 2-APB (32μM) also augmented the SRREF by ~170% and ~71%, respectively. Methoxyverapamil (D-600, an L-type Ca2+ channel blocker), 2-APB (100µM, antagonist of the capacitative Ca2+ entry) and PPADS (NCXREV blocker) diminished the SRREF by ~63%, ~72% and ~31%, respectively. The simultaneous addition of D-600 and 2-APB annulled SRREF. These last results were also seen when carbachol was used instead of caffeine. In tracheal rings, 2-APB and nifedipine abolished the carbachol-induced contraction. We concluded that the sarcoplasmic reticulum Ca2+ pump is the only mechanism involved in the SRREF and that L-type Ca2+ voltage dependent and store operated Ca2+ channels are the principal membranal Ca2+ handling proteins that provide extracellular Ca2+ for SRREF and carbachol-induced contraction in the guinea pig airway smooth muscle; NCXREV seems to play a minor role.

A synthetic compound, 4-acetyl-3-methyl-6-(3,4,5-trimethoxyphenyl)pyrano[3,4-c]pyran-1,8-dione, ameliorates ovalbumin-induced asthma

Eosinophilia is one of the characteristic signs of allergic inflammation. Massive migration of eosinophils to the airways can cause epithelial tissue injury, contraction of airway smooth muscle and increased bronchial responsiveness. Previously, we discovered a new compound, 1H,8H-pyrano[3,4-c]pyran-1,8-dione (PPY), derived from the fruit of Vitex rotundifolia L. and evaluated its anti-inflammatory and anti-asthmatic properties. In this study, we synthesized a new modified compound, 4-acetyl-3-methyl-6-(3,4,5-trimethoxyphenyl) pyrano[3,4-c]pyran-1,8-dione (PPY-345), which was based on the PPY skeleton, and we evaluated its anti-asthmatic effects. To evaluate the anti-asthmatic effect of PPY-345 in vitro, A549 lung epithelial cells were stimulated with TNF-alpha, IL-4 and IL-1-beta to induce the expression of CCL11 (Eotaxin), a chemokine involved in eosinophil chemotaxis. To characterize the anti-asthmatic properties of PPY-345 in vivo, we examined the influence of PPY-345 in an ovalbumin (OVA)-induced asthma model. PPY-345 treatments significantly reduced CCL11 secretion. PPY-345 treatment did not inhibit the translocation of NF-κB into the nucleus but suppressed the phosphorylation of signal transducers and activators of transcription 6 (STAT6). PPY-345 treatment significantly reduced airway hyperreactivity as measured by whole-body plethysmography. PPY-345 further reduced total cells, including eosinophil, macrophage and lymphocytes, in the BAL fluid, goblet cell hyperplasia and myosin light chain 2 positive smooth muscle cell area in the lung tissue. Additionally, PPY-345 significantly suppressed the levels of OVA–IgE present in the serum. These results suggested that PPY-345 could improve asthma symptoms in OVA-sensitized mice.

The Sophora flavescens flavonoid compound trifolirhizin inhibits acetylcholine induced airway smooth muscle contraction.

Asthma is a serious health problem worldwide, particularly in industrialized countries. Despite a better understanding of the pathophysiology of asthma, there are still considerable gaps in knowledge as well as a need for classes of drugs. ASHMI™ (Anti-asthma Herbal Medicine Intervention) is an aqueous extract of Ganoderma lucidum (Fr.) P. Karst (Ling Zhi), Sophora flavescens Aiton (Ku Shen) and Glycyrrhiza uralensis Fisch. ex DC (Gan Cao). It prevents allergic asthma airway hyper-reactivity in mice and inhibits acetylcholine (ACh) induced airway smooth muscle (ASM) contraction in tracheal rings from allergic asthmatic mice. The purpose of this research was to identify individual herb(s) and their active compound(s) that inhibit ASM contraction. It was found that S. flavescens, but not G. lucidum or G. uralensis aqueous extracts, inhibited ASM contraction in tracheal rings from asthmatic mice. Bioassay-guided isolation and identification of flavonoid fractions/compound(s) via methylene chloride extraction, preparative HPLC fractionation, and LC-MS and NMR spectroscopic analyses showed that trifolirhizin is an active constituent that inhibits acetylcholine mediated ASM contraction or directly relaxes pre-contracted ASM independent of β2-adrenoceptors.

Neurotransmitters in parasympathetic ganglionic neurons and nerves in mouse lower airway smooth muscle

In most species, including humans, lower airway smooth muscle (ASM) contains nerve terminals from two distinct populations of parasympathetic ganglionic neurons based on neurotransmitter phenotype: cholinergic and non-adrenergic non-cholinergic (NANC), causing contraction and relaxation, respectively, of ASM. Using immunohistological staining, the density and distribution of NANC-associated neurotransmitters, vasoactive intestinal peptide (VIP) and nitric oxide synthase were 6% of total nerve profiles compared to 19% cholinergic nerves in ASM in mouse (C57BL/6) central airways. The location of the NANC parasympathetic neurons innervating the tracheal ASM, as determined by retrograde neuronal tracer from the trachealis muscle, was the myenteric plexus of the esophagus, closely associated with the outer striated longitudinal muscle layers; the majority of the retrograde-labeled neurons were VIP- and NOS-IR. The results of these experiments provide the first direct evidence that VIP-IR and NOS-IR neurons intrinsic to the mouse esophagus project axons to the adjacent trachealis muscle.

Exercise and airway injury in athletes.

Olympic level athletes present an increased risk for asthma and allergy, especially those who take part in endurance sports, such as swimming or running, and in winter sports. Classical postulated mechanisms behind EIA include the osmotic, or airway-drying, hypothesis. Hyperventilation leads to evaporation of water and the airway surface liquid becomes hyperosmolar, providing a stimulus for water to move from any cell nearby, which results in the shrinkage of cells and the consequent release of inflammatory mediators that cause airway smooth muscle contraction. But the exercise-induced asthma/bronchoconstriction explanatory model in athletes probably comprises the interaction between environmental training factors, including allergens and ambient conditions such as temperature, humidity and air quality; and athlete's personal risk factors, such as genetic and neuroimmuneendocrine determinants. After the stress of training and competitions athletes experience higher rate of upper respiratory tract infections (URTI), compared with lesser active individuals. Increasing physical activity in non-athletes is associated with a decreased risk of URTI. Heavy exercise induces marked immunodepression which is multifactorial in origin. Prolonged, high intensity exercise temporarily impairs the immune competence while moderate activity may enhance immune function. The relationship between URTI and exercise is affected by poorly known individual determinants such genetic susceptibility, neurogenic mediated immune inflammation and epithelial barrier dysfunction. Further studies should better define the aetiologic factors and mechanisms involved in the development of asthma in athletes, and propose relevant preventive and therapeutic measures.

Hydrogen sulfide induces smooth muscle relaxation in small intrapulmonary airways

Hydrogen sulfide (H2S) has been recognized recently as a gaseous signaling molecule that has a variety of physiological functions. However, the role of H2S in the respiratory system is not fully understood. We used mouse lung slices to study the effect of H2S on airway smooth muscle contraction. Perfusion of lung slices with 100 μM Na2S (a H2S donor) induced ~60% relaxation of airways pre‐contracted with 100 nM ACh. A similar H2S‐induced relaxation was observed in airways pre‐contracted with 5‐HT. H2S‐induced relaxation was sustained, reversible, and concentration‐dependent. Furthermore, H2S right‐shifted the ACh concentration‐contraction curve and decreased the maximal airway contraction. Similar to H2S, addition of 10 mM L‐cysteine (Cys) –a precursor of the H2S biosynthesis, strongly relaxed ACh‐contracted airways. In contrast, 10 mM L‐serine induced small airway relaxation. Furthermore, Cys‐induced airway relaxation was inhibited by propargylglycine (PPG), an inhibitor of the H2S synthesizing enzyme cystathionine γ‐lyase (CSE). The mechanism of H2S‐induced airway relaxation is currently being investigated. In conclusion, H2S has bronchodilator properties by inducing strong relaxation in small airways. Supported by the American Lung Association & American Heart Association.