Neural control of goblet cell secretion in guinea pig airways

Early studies on the surface epithelium of mammalian airways

This article traces the beginnings of the various areas of physiological research on airway epithelium. First mentioned in 1600, it was not until 1834 that it was found to be ciliated. Goblet and basal cells were described in 1852, to be followed by ~10 other epithelial cell types (the most recent in 2018). It also contains nerve endings and resident leukocytes. Mucociliary clearance was documented in 1835, but the first studies on the ciliary beat cycle did not appear until 1890, and a definitive description was not published until 1981. It was established in 1932 that goblet cells in the cat trachea were unresponsive to cholinergic agents; but only since 1980 or so has any significant progress been made on what does cause them to degranulate. Active transfer of salts across epithelia creates local osmotic gradients that drive transepithelial water flows. Vectorial salt transport was first described for airway epithelium in 1968, and the associated volume flows were measured in 1981. Evidence that airway epithelium releases signaling molecules first appeared in 1981. Since then, scores of molecules have been identified. The pace of research in most areas increased dramatically after the development of confluent, polarized cultures of airway epithelium in the early 1980s.

Neuropeptides in asthma, chronic obstructive pulmonary disease and cystic fibrosis

The nervous system mediates key airway protective behaviors, including cough, mucus secretion, and airway smooth muscle contraction. Thus, its involvement and potential involvement in several airway diseases has become increasingly recognized. In the current review, we focus on the contribution of select neuropeptides in three distinct airway diseases: asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. We present data on some well-studied neuropeptides, as well as call attention to a few that have not received much consideration. Because mucus hypersecretion and mucus obstruction are common features of many airway diseases, we place special emphasis on the contribution of neuropeptides to mucus secretion. Finally, we highlight evidence implicating involvement of neuropeptides in mucus phenotypes in asthma, COPD and cystic fibrosis, as well as bring to light knowledge that is still lacking in the field.

Mechanisms of airway responses to esophageal acidification in cats

Acid in the esophagus causes airway constriction, tracheobronchial mucous secretion, and a decrease in tracheal mucociliary transport rate. This study was designed to investigate the neuropharmacological mechanisms controlling these responses. In chloralose-anesthetized cats (n = 72), we investigated the effects of vagotomy or atropine (100 μg·kg(-1)·30 min(-1) iv) on airway responses to esophageal infusion of 0.1 M PBS or 0.1 N HCl at 1 ml/min. We quantified 1) diameter of the bronchi, 2) tracheobronchial mucociliary transport rate, 3) tracheobronchial mucous secretion, and 4) mucous content of the tracheal epithelium and submucosa. We found that vagotomy or atropine blocked the airway constriction response but only atropine blocked the increase in mucous output and decrease in mucociliary transport rate caused by esophageal acidification. The mucous cells of the mucosa produced more Alcian blue- than periodic acid-Schiff (PAS)-stained mucosubstances, and the mucous cells of the submucosa produced more PAS- than Alcian blue-stained mucosubstances. Selective perfusion of the different segments of esophagus with HCl or PBS resulted in significantly greater production of PAS-stained mucus in the submucosa of the trachea adjacent to the HCl-perfused esophagus than in that adjacent to the PBS-perfused esophagus. In conclusion, airway constriction caused by esophageal acidification is mediated by a vagal cholinergic pathway, and the tracheobronchial transport response is mediated by cholinergic receptors. Acid perfusion of the esophagus selectively increases production of neutral mucosubstances of the apocrine glands by a local mechanism. We hypothesize that the airway responses to esophageal acid exposure are part of the innate, rather than acute emergency, airway defense system.

Airway Gland Structure and Function

Submucosal glands contribute to airway surface liquid (ASL), a film that protects all airway surfaces. Glandular mucus comprises electrolytes, water, the gel-forming mucin MUC5B, and hundreds of different proteins with diverse protective functions. Gland volume per unit area of mucosal surface correlates positively with impaction rate of inhaled particles. In human main bronchi, the volume of the glands is ∼ 50 times that of surface goblet cells, but the glands diminish in size and frequency distally. ASL and its trapped particles are removed from the airways by mucociliary transport. Airway glands have a tubuloacinar structure, with a single terminal duct, a nonciliated collecting duct, then branching secretory tubules lined with mucous cells and ending in serous acini. They allow for a massive increase in numbers of mucus-producing cells without replacing surface ciliated cells. Active secretion of Cl(-) and HCO3 (-) by serous cells produces most of the fluid of gland secretions. Glands are densely innervated by tonically active, mutually excitatory airway intrinsic neurons. Most gland mucus is secreted constitutively in vivo, with large, transient increases produced by emergency reflex drive from the vagus. Elevations of [cAMP]i and [Ca(2+)]i coordinate electrolyte and macromolecular secretion and probably occur together for baseline activity in vivo, with cholinergic elevation of [Ca(2+)]i being mainly responsive for transient increases in secretion. Altered submucosal gland function contributes to the pathology of all obstructive diseases, but is an early stage of pathogenesis only in cystic fibrosis.

Sex- and afferent-specific differences in histamine receptor expression in vagal afferents of rats: A potential mechanism for sexual dimorphism in prevalence and severity of asthma

The incidence of asthma is more common in boys than in girls during the childhood, and more common in premenopausal female than age-matched males. Our previous study demonstrated a gender difference in histamine-mediated neuroexcitability in nodose ganglia neurons (NGNs), highlighting a possibility of histamine-mediated gender difference in asthma via visceral afferent function. In the present study, we aimed to explore the gender difference in expression profiles of histamine receptors (HRs) in nodose ganglia (NG) and individual identified NGNs to provide deeper insights into the mechanisms involved in sexual dimorphism of asthma. Western-blot and SYBR green RT-PCR showed that H2R and H3R were highly expressed in NG of females compared with males and downregulated in ovariectomized females. H1R was equally expressed in NG of both sexes and not altered by ovariectomy. Furthermore, this highly expressive H2R and H3R were distributed in both myelinated and unmyelinated NGNs isolated from adult female rats by immunofluorescence and single-cell RT-PCR. H3R widely distributed in all tested neuron subtypes and its expression did not show significant difference among neuron subtypes. H2R was widely and highly expressed in low-threshold and sex-specific subpopulation of myelinated Ah-types compared with myelinated A- and unmyelinated C-type NGNs. Unexpectedly, weak expression of H1R was detected in both myelinated and unmyelinated NGNs by immunofluorescence, which was further confirmed by single-cell RT-PCR. Our results suggest that the sexual dimorphism in the expression of H2R and H3R in vagal afferents very likely contributes, at least partially, to the gender difference in prevalence and severity of asthma.

Cholinergic regulation of epithelial sodium channels in rat alveolar type 2 epithelial cells

We and others have shown that epithelial Na(+) channels (ENaC) in alveolar type 2 (AT2) cells are activated by β2 agonists, steroid hormones, elevated oxygen tension, and by dopamine. Although acetylcholine receptors (AChRs) have been previously described in the lung, there are few reports of whether cholinergic agonists alter sodium transport in the alveolar epithelium. Therefore, we investigated how cholinergic receptors regulate ENaC activity in primary cultures of rat AT2 cells using cell-attached patch-clamp recordings to assess ENaC activity. We found that the muscarinic agonists, carbachol (CCh) and oxotremorine, activated ENaC in a dose-dependent manner but that nicotine did not. CCh-induced activation of ENaC was blocked by atropine. Western blotting and immunohistochemistry suggested that muscarinic M2 and M3 receptors (mAChRs) but not nicotinic receptors were present in AT2 cells. Endogenous RhoA and GTP-RhoA increased in response to CCh and the increase was reduced by pretreatment with atropine. We showed that Y-27632, an inhibitor of Rho-associated protein kinase (ROCK), abolished endogenous ENaC activity and inhibited the activation of ENaC by CCh. We also showed that ROCK signaling was necessary for ENaC stability in 2F3 cells, a model for AT2 cells. Our results showed that muscarinic agonists activated ENaC in rat AT2 cells through M2 and/or M3 mAChRs probably via a RhoA/ROCK signaling pathway.

Histamine-induced changes in rat tracheal goblet cell mucin store and mucosal edema

The pathology of chronic asthma in human and mouse is characterized by inflammation and remodeling of airway tissues. As a result of repeated inflammatory insults to the lower airways, smooth muscle thickening, mucin secretion and airway hyperreactivity may develop. In ovalbumin (OVA)-sensitized mice with repeated challenges with OVA to the lower airways, the trachea and bronchi are characterized by goblet cell hyperplasia and mucus hypersecretion from goblet cells. Previous study reports that intravenous (i.v.) application of a high dose of capsaicin releases tachykinin from capsaicin-sensitive nerves, producing acute plasma leakage and mucosal edema formation and causing depletion of mucin granules in goblet cells that results in a reduction in the number and size of Alcian blue (AB)-positive goblet cells in the rat trachea within a few minute after capsaicin application. Histamine is an important non-neural mediator of asthma from mast cells. The present study investigated whether i.v. application of a high dose of histamine (18 μmol/ml/kg) could result in these acute changes and the similar time-course changes in rat trachea. The tracheal whole mounts stained with chloroacetate esterase reagent and AB and tracheal methacrylate sections stained with AB and periodic acid-Schiff reagent were used for evaluation of histological and cellular changes. At 5 min after histamine application, mucosal leaky venules were numerous and subepithelial edema ratio (% of length of edema along the mucosal epithelial circumference of tracheal cross section) was found to be 48.2 ± 4.9, which was greater (P < 0.01) than saline-treated rats. But, the number of AB-positive goblet cells, 2,030 ± 170/mm(2) of mucosal surface epithelium, was similar to saline-treated group (P > 0.05). One day later, edema ratio remained large and the number of AB-positive goblet cells was 1,140 ± 150/mm(2) epithelium, reduced to half the number of the group at 5 min after histamine (P < 0.01). It is suggested that mucus hypersecretion occurred at this time point. At 3 or 5 days after histamine, edema ratio gradually decreased. The number of AB-positive goblet cells continued to remain small on day 3. On day 5 after histamine, the number of AB-positive goblet cells restored to the level of rat group at 5 min after histamine application. At 7 days after histamine, edema ratio returned to the level of saline-treated group. It is concluded that degranulation and thinning of tracheal goblet cells and mucus hypersecretion lagged behind histamine-induced acute plasma leakage and edema, and restoration of mucin store in goblet cells was associated with remission of mucosal edema.

Effect of disodium cromoglycate on airway mucus secretion during antigen-induced late asthmatic responses in a murine model of asthma

BACKGROUND

Disodium cromoglycate (DSCG) is known to inhibit both immediate and late asthmatic responses (IAR and LAR). However, its effect on mucus hypersecretion is unknown. Using a murine model of asthma, we aimed to determine whether mucus secretion increased during IAR and LAR. We also studied the potency of DSCG in inhibiting mucus secretion and on airway eosinophilia.

METHODS

Mice were subjected to initial intraperitoneal sensitization and airway challenge to ovalbumin (OVA) and then provoked by additional exposure to OVA. Some mice were pretreated with aerosolized DSCG (20 mg/ml) 1 h before the provocation with OVA. After serial measurements of enhanced pause (Penh), an indicator of airflow obstruction, serum samples and bronchoalveolar lavage fluids (BALF) were collected. Then, the lungs were excised and a morphometric analysis for mucus hypersecretion was performed.

RESULTS

A biphasic increase in Penh (IAR and LAR) was observed in sensitized animals after provocation with OVA. Airway eosinophilia was observed during both responses. Intraluminal mucus significantly increased during LAR, but not during IAR. DSCG significantly attenuated both IAR and LAR, and significantly inhibited the increase in intraluminal mucus during LAR, but had no effect on eosinophilia in BALF.

CONCLUSION

Our results suggest that airway hypersecretion may be involved as a component of airflow obstruction during LAR, and that this is unlikely during IAR. DSCG may be effective in reducing excessive airway mucus caused by exposure to allergens.

Disruptive effects of anion secretion inhibitors on airway mucus morphology in isolated perfused pig lung

Since anion secretion inhibitors reproduce important aspects of cystic fibrosis (CF) lung disease, the effects of these antagonists on airway mucus morphology were assessed in isolated perfused pig lungs. Maximal inhibitory concentrations of bumetanide and dimethylamiloride, which respectively block Cl- and HCO3- secretion in porcine airways, induced the formation of dense 'plastered' mucus on the airway surface, depletion of periciliary fluid and collapse of cilia. This effect was more pronounced when lungs were also exposed to bethanechol to stimulate submucosal gland secretion, when plastered mucus covered > 98 % of the airway surface. Bethanechol also reduced gland duct mucin content in the absence, but not presence, of the anion secretion inhibitors. Anion secretion inhibitors did not induce measurable increases in goblet cell degranulation. We conclude that inhibition of anion and liquid secretion in porcine lungs disrupts the normal morphology of airway surface mucus, providing further evidence that impaired anion secretion alone could account for critical aspects of CF lung disease.

P2Y(2) receptor-stimulated phosphoinositide hydrolysis and Ca(2+) mobilization in tracheal epithelial cells

Extracellular nucleotides have been implicated in the regulation of secretory function through the activation of P2 receptors in the epithelial tissues, including tracheal epithelial cells (TECs). In this study, experiments were conducted to characterize the P2 receptor subtype on canine TECs responsible for stimulating inositol phosphate (InsP(x)) accumulation and Ca(2+) mobilization using a range of nucleotides. The nucleotides ATP and UTP caused a concentration-dependent increase in [(3)H]InsP(x) accumulation and Ca(2+) mobilization with comparable kinetics and similar potency. The selective agonists for P1, P2X, and P2Y(1) receptors, N(6)-cyclopentyladenosine and AMP, alpha,beta-methylene-ATP and beta, gamma-methylene-ATP, and 2-methylthio-ATP, respectively, had little effect on these responses. Stimulation of TECs with maximally effective concentrations of ATP and UTP showed no additive effect on [(3)H]InsP(x) accumulation. The response of a maximally effective concentration of either ATP or UTP was additive to the response evoked by bradykinin. Furthermore, ATP and UTP induced a cross-desensitization in [(3)H]InsP(x) accumulation and Ca(2+) mobilization. These results suggest that ATP and UTP directly stimulate phospholipase C-mediated [(3)H]InsP(x) accumulation and Ca(2+) mobilization in canine TECs. P2Y(2) receptors may be predominantly mediating [(3)H]InsP(x) accumulation, and, subsequently, inositol 1,4,5-trisphosphate-induced Ca(2+) mobilization may function as the transducing mechanism for ATP-modulated secretory function of tracheal epithelium.

Effect of long term treatment with oxitropium bromide on airway secretion in chronic bronchitis and diffuse panbronchiolitis

BACKGROUND

Anticholinergic bronchodilator drugs improve lung function in chronic bronchitis but less is known of their effects on the volume and physical properties of sputum in conditions associated with excessive airway secretions. This study examines the effects of the regular use of oxitropium bromide in such patients.

METHODS

The study was conducted in a parallel, double blind, placebo controlled fashion. Patients were divided into two groups: the first group (n = 17) received oxitropium bromide from a metered dose inhaler (two puffs three times daily; 100 micrograms/puff) for eight weeks, and the second group (n = 16) received placebo. Lung function was measured as forced expiratory volume in one second (FEV1) and vital capacity. In evaluating airway secretion, daily amount of expectorated sputum, percentage solid composition, viscoelastic properties including elastic modulus and dynamic viscosity, and sputum microbiology were determined.

RESULTS

Oxitropium bromide increased FEV1 and decreased the mean (SE) sputum production from 61(4) to 42(3) g/day after treatment, whereas placebo had no effect. Bacterial density and sputum flora were unchanged, but solid composition and elastic modulus increased from 2.52(0.43)% to 3.12(0.34)%, and 68(12) dyne/cm2, respectively, in the group taking oxitropium bromide.

CONCLUSIONS

Regular treatment with oxitropium bromide not only improves airflow limitation but also reduces sputum production, probably through the inhibition of both mucus secretion and water transport, the latter component being predominant.

Attenuation of tachykinin-induced airflow obstruction and microvascular leakage in immature airways

1. To study the effect of maturation on substance P (SP)- and neurokinin A (NKA)-induced airflow obstruction and airway microvascular leakage (MVL), we have measured changes in both lung resistance (RL) and extravasation of Evans blue dye in anaesthetized immature (aged 14 +/- 1 days) and adult guinea-pigs (aged 80 +/- 3 days). 2. RL and its recovery after hyperinflation at 5 min were measured for 6 min after i.v. SP (0.2, 1 and 30 nmol kg-1), NKA (1 and 10 nmol kg-1) or vehicle (0.9% NaCl). After measurement of RL, MVL in trachea, main bronchi and intrapulmonary airways was also examined. 3. The order of potency in inducing airflow obstruction did not change with age (NKA > SP) but immature animals required a larger dose of SP or NKA than adults to cause a significant increase in RL. 4. The order of potency in inducing airway microvascular leakage was SP > NKA in both immature and adult animals. The amount of extravasated dye after SP was significantly less in immature airways, especially in central airways. 5. Phosphoramidon (2.5 mg kg-1), a neutral endopeptidase (NEP) inhibitor, significantly increased RL after 0.2 nmol kg-1 SP only in adult airways. Phosphoramidon enhanced the dye extravasation after 0.2 nmol kg-1 SP in both immature and adult airways with a significantly greater amount of dye in adult animals, suggesting that mechanisms other than changes in NEP activity may be responsible for this age-related difference. 6. RL after hyperinflation following SP was not correlated with the degree of extravasation of Evans blue dye in immature animals, whereas it was closely correlated in adult animals. 7. SP and NKA may be less potent in causing both bronchoconstriction and microvascular leakage in immature airways. 8. Airway oedema caused by microvascular leakage may contribute less in immature airways to airflow obstruction after SP or NKA.

Unilateral cervical vagotomy decreases the magnitude of neurogenic inflammation induced by capsaicin in the ipsilateral bronchial tree of rats

Electrical stimulation of a single cervical vagus nerve produces neurogenic inflammation on the stimulated side of the bronchial tree, including the first (main) to the 4th order bronchi. In the contralateral bronchial tree, in contrast, only the proximal part of the main bronchus exhibits inflammatory changes, suggesting that vagal sensory axons present in the bronchi largely originate from the ipsilateral vagus nerve. Intravenous administration of capsaicin can evoke neurogenic inflammation in bilateral bronchial trees. Sensory axons from various sources are thought to be stimulated by this irritant. The extent to which neurogenic inflammation in both bronchial trees might be reduced by unilateral vagotomy is not known. In the present study, we sought to characterize the effect of unilateral cervical vagotomy on capsaicin-induced changes in plasma extravasation and secretory activity of goblet cells in the bronchial trees of both sides. To quantify the magnitude of neurogenic plasma extravasation, Evans blue was used as a tracer dye to measure spectrophotometrically its amount in the bronchial wall. Another tracer dye, Monastral blue, was used to localize the distribution of leaky blood vessels and to measure morphometrically their area density in the whole mounts. To investigate cell and tissue responses of the mucosa, histological methods were employed. After 2 or 4 postoperative weeks, the rats were intravenously administered with a single dose of capsaicin, 150 micrograms/kg. This resulted in different magnitudes of Evans blue extravasation in the bronchi of the two sides in vagotomized rats. Extravasation of Evans blue dye in the bronchial tree ipsilateral to vagotomy was one-half to two-thirds of that of the contralateral bronchial tree.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential inhibitory effects of opioids on cigarette smoke, capsaicin and electrically-induced goblet cell secretion in guinea-pig trachea

1. Goblet cell secretion in guinea-pig airways is under neural control. Opioids have previously been shown to inhibit neurogenic plasma exudation and bronchoconstriction in guinea-pig airways. We have now examined the effects of morphine and opioid peptides on tracheal goblet cell secretion induced by either electrical stimulation of the cervical vagus nerves, exogenous capsaicin, or acute inhalation of cigarette smoke. The degree of goblet cell secretion was determined by a morphometric method and expressed as a mucus score which is inversely related to mucus discharge. 2. Morphine, 1 mg kg-1, completely blocked goblet cell secretion induced by electrical stimulation of the vagus nerves. Morphine also inhibited the response to cigarette smoke given either at a low dose (10 breaths of 1:10 diluted in air), which principally activates cholinergic nerves, or at a high dose (20 breaths of undiluted), which activates capsaicin-sensitive sensory nerves, by 100% and 73% respectively. In contrast, morphine had no significant inhibitory effect on capsaicin-induced goblet cell secretion. The inhibitory effect of morphine was reversed by naloxone. 3. Selective mu- or delta-opioid receptor agonists, [D-Ala2, NMePhe4, Glyol5]enkephalin (DAMGO) or [D-Pen2, D-Pen5]enkephalin (DPDPE) respectively, caused a dose-related inhibition of low dose cigarette smoke-induced goblet cell discharge, with DPDPE more potent than DAMGO. A kappa-receptor agonist, trans-3,4-dichloro-N-methyl-N-(2-(1-pyrollidinyl)cyclohexyl) benzeneacetamine (U-50,488H), had no inhibitory effect. DPDPE had no inhibitory effect on goblet cell secretion induced by exogenous methacholine. 4. DAMGO dose-dependently blocked the response to high dose cigarette smoke with a maximal inhibition of 95% at 2 x 10(-7) mol kg-1. Neither DPDPE nor U-50,488H had any significant inhibitory effect. The increase in goblet cell secretion induced by exogenous substance P was not affected by DAMGO.5. We conclude that opioids inhibit neurally-mediated goblet cell secretion via actions at prejunctional delta and mu-receptors on cholinergic nerves and at mu-receptors on sensory nerve endings, and that capsaicin activation of sensory nerves is via a different mechanism from that of electrical or cigarette smoke activation.

Capsaicin and sensory neuropeptide stimulation of goblet cell secretion in guinea-pig trachea

1. We studied the effect of capsaicin and sensory neuropeptides on tracheal goblet cell secretion in anaesthetized guinea-pigs using a semi-quantitative morphometric technique whereby the magnitude of discharge of stained intracellular mucus, expressed as a mucus score (MS), was related inversely to discharge. 2. Capsaicin (i.v.) induced goblet cell secretion: a decrease of 50% in MS below control (indicative of increased secretion) was maximal at 3.3 x 10(-9) mol/kg. 3. Capsaicin-induced secretion was unaffected either by prior vagus nerve section or by pre-treatment with atropine, propranolol and phentolamine which suggests that local axon reflexes with release of sensory neuropeptides are involved in the response. 4. Intravenous substance P (SP), neurokinin A (NKA), neurokinin B (NKB), and calcitonin gene-related peptide (CGRP) produced dose-related increases in goblet cell secretion, with SP the most potent. Doses (mol/kg) causing a 50% decrease in MS from control were 3.5 x 10(-12) for SP; 72 x 10(-10) for NKA; 1.6 x 10(-9) for NKB; and 1.2 x 10(-8) for CGRP. The maximal increase in goblet cell secretion was 75% of control and occurred with SP at 10(-10) mol/kg. 5. SP-induced mucus discharge was not inhibited by atropine or the histamine receptor antagonists mepyramine or cimetidine. 6. We conclude that in guinea-pig trachea, goblet cell secretion is under the control of capsaicin-sensitive sensory nerves and release of neuropeptides from these nerves may induce mucus discharge via tachykinin receptors of the NK-1 subtype (indicated by an order of potency of SP greater than NKA greater than NKB).