An in vivo guinea pig preparation for studying the autonomic regulation of airway smooth muscle tone

Airway levels of the endogenous bronchodilator S-nitrosoglutathione (GSNO) are low in children with near-fatal asthma. We hypothesized that GSNO could be broken down in the lung and that this catabolism could inhibit airway smooth muscle relaxation. In our experiments, GSNO was broken down by guinea pig lung homogenates, particularly after ovalbumin sensitization (OS). Two lung protein fractions had catabolic activity. One was NADPH dependent and was more active after OS. The other was NADPH independent and was partially inhibited by aurothioglucose. Guinea pig lung tissue protein fractions with GSNO catabolic activity inhibited GSNO-mediated guinea pig tracheal ring relaxation. The relaxant effect of GSNO was partially restored by aurothioglucose. These observations suggest that catabolism of GSNO in the guinea pig 1) is mediated by lung proteins, 2) is partially upregulated after OS, and 3) may contribute to increased airway smooth muscle tone. We speculate that enzymatic breakdown of GSNO in the lung could contribute to asthma pathophysiology by inhibiting the beneficial effects of GSNO, including its effect on airway smooth muscle tone.

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Melatonin MT2 receptor is expressed and potentiates contraction in human airway smooth muscle

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00273.2021 ◽

2021 ◽

Author(s):

Haruka Sasaki ◽

Yi Zhang ◽

Charles W Emala ◽

Kentaro Mizuta

Keyword(s):

Smooth Muscle ◽

Guinea Pig ◽

Airway Smooth Muscle ◽

Muscle Tone ◽

Fiber Formation ◽

Melatonin Receptors ◽

Human Airway Smooth Muscle ◽

Nocturnal Asthma ◽

Smooth Muscle Tone ◽

Human Airway

Nocturnal asthma is characterized by heightened bronchial reactivity at night, and plasma melatonin concentrations are higher in patients with nocturnal asthma symptoms. Numerous physiological effects of melatonin are mediated via its specific G protein-coupled receptors (GPCRs) named the MT1 receptor which couples to both Gq and Gi proteins, and the MT2 receptor which couples to Gi. We investigated whether melatonin receptors are expressed on airway smooth muscle, whether they regulate intracellular cyclic AMP (cAMP) and calcium concentrations ([Ca2+]i) which modulate airway smooth muscle tone, and whether they promote airway smooth muscle cell proliferation. We detected the mRNA and protein expression of the melatonin MT2 but not the MT1 receptor in native human and guinea pig airway smooth muscle and cultured human airway smooth muscle (HASM) cells by RT-PCR, immunoblotting, and immunohistochemistry. Activation of melatonin MT2 receptors with either pharmacological concentrations of melatonin (10 - 100 µM) or the non-selective MT1/MT2 agonist ramelteon (10 µM) significantly inhibited forskolin-stimulated cAMP accumulation in HASM cells, which was reversed by the Gαi protein inhibitor pertussis toxin or knockdown of the MT2 receptor by its specific siRNA. Although melatonin by itself did not induce an initial [Ca2+]i increase and airway contraction, melatonin significantly potentiated acetylcholine-stimulated [Ca2+]i increases, stress fiber formation through the MT2 receptor in HASM cells, and attenuated the relaxant effect of isoproterenol in guinea pig trachea. These findings suggest that the melatonin MT2 receptor is expressed in ASM, and modulates airway smooth muscle tone via reduced cAMP production and increased [Ca2+]i.

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Inhibition of dihydropyridine-sensitive calcium entry in hypoxic relaxation of airway smooth muscle

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1995.268.2.l201 ◽

1995 ◽

Vol 268 (2) ◽

pp. L201-L206 ◽

Cited By ~ 2

Author(s):

C. Vannier ◽

T. L. Croxton ◽

L. S. Farley ◽

C. A. Hirshman

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Muscle Tone ◽

Bay K 8644 ◽

O2 Concentration ◽

Voltage Dependent ◽

Progressive Hypoxia ◽

Carbamyl Choline

Hypoxia dilates airways in vivo and reduces active tension of airway smooth muscle in vitro. To determine whether hypoxia impairs Ca2+ entry through voltage-dependent channels (VDC), we tested the ability of dihydropyridines to modulate hypoxia-induced relaxation of KCl- and carbamyl choline (carbachol)-contracted porcine bronchi. Carbachol- or KCl-contracted bronchial rings were exposed to progressive hypoxia in the presence or absence of 1 microM BAY K 8644 (an L-type-channel agonist). In separate experiments, rings were contracted with carbachol or KCl, treated with nifedipine (a VDC antagonist), and finally exposed to hypoxia. BAY K 8644 prevented hypoxia-induced relaxation in KCl-contracted bronchi. Nifedipine (10(-5) M) totally relaxed KCl- contracted bronchi. Carbachol-contracted bronchi were only partially relaxed by nifedipine but were completely relaxed when the O2 concentration of the gas was reduced from 95 to 0%. These data indicate that hypoxia can reduce airway smooth muscle tone by limiting entry of Ca2+ through a dihydropyridine-sensitive pathway, but that other mechanisms also contribute to hypoxia-induced relaxation of carbachol-contracted bronchi.

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A smooth muscle tone-dependent stretch-activated migrating motor pattern in isolated guinea-pig distal colon

The Journal of Physiology ◽

10.1113/jphysiol.2003.049163 ◽

2003 ◽

Vol 551 (3) ◽

pp. 955-969 ◽

Cited By ~ 38

Author(s):

T. K Smith ◽

G. R Oliver ◽

G. W Hennig ◽

D. M O'Shea ◽

P. V. Berghe ◽

...

Keyword(s):

Smooth Muscle ◽

Guinea Pig ◽

Muscle Tone ◽

Motor Pattern ◽

Distal Colon ◽

Smooth Muscle Tone

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A GABAergic inhibitory microcircuit controlling cholinergic outflow to the airways

Journal of Applied Physiology ◽

10.1152/japplphysiol.00523.2003 ◽

2004 ◽

Vol 96 (1) ◽

pp. 260-270 ◽

Cited By ~ 29

Author(s):

Constance T. Moore ◽

Christopher G. Wilson ◽

Catherine A. Mayer ◽

Sandra S. Acquah ◽

V. John Massari ◽

...

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Muscle Tone ◽

Structural Characteristics ◽

Nucleus Ambiguus ◽

Acid Decarboxylase ◽

Electron Microscopic ◽

Synaptic Contacts ◽

Smooth Muscle Tone ◽

Rostral Nucleus

GABA is the main inhibitory neurotransmitter that participates in the regulation of cholinergic outflow to the airways. We have tested the hypothesis that a monosynaptic GABAergic circuit modulates the output of airway-related vagal preganglionic neurons (AVPNs) in the rostral nucleus ambiguus by using a dual-labeling electron microscopic method combining immunocytochemistry for glutamic acid decarboxylase (GAD) with retrograde tracing from the trachea. We also determined the effects of blockade of GABAA receptors on airway smooth muscle tone. The results showed that retrogradely labeled AVPNs received a significant GAD-immunoreactive (GAD-IR) terminal input. Out of a pooled total of 3,161 synaptic contacts with retrogradely labeled somatic and dendritic profiles, 20.2% were GAD-IR. GAD-IR terminals formed significantly more axosomatic synapses than axodendritic synapses ( P < 0.02). A dense population of GABAergic synaptic contacts on AVPNs provides a morphological basis for potent physiological effects of GABA on the excitability of AVPNs. GAD-IR terminals formed exclusively symmetric synaptic specializations. GAD-IR terminals were significantly larger ( P < 0.05) in both length and width than unlabeled terminals synapsing on AVPNs. Therefore, the structural characteristics of certain nerve terminals may be closely correlated with their function. Pharmacological blockade of GABAA receptors within the rostral nucleus ambiguus increased activity of putative AVPNs and airway smooth muscle tone. We conclude that a tonically active monosynaptic GABAergic circuit utilizing symmetric synapses regulates the discharge of AVPNs.

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Airway basement membrane perimeter in human airways is not a constant; potential implications for airway remodeling in asthma

Journal of Applied Physiology ◽

10.1152/japplphysiol.00982.2003 ◽

2004 ◽

Vol 97 (2) ◽

pp. 556-563 ◽

Cited By ~ 12

Author(s):

Brent E. McParland ◽

Peter D. Paré ◽

Peter R. A. Johnson ◽

Carol L. Armour ◽

Judith L. Black

Keyword(s):

Smooth Muscle ◽

Basement Membrane ◽

Airway Smooth Muscle ◽

Muscle Tone ◽

Airway Remodeling ◽

Organ Bath ◽

Smooth Muscle Tone ◽

Asthmatic Patients ◽

Constant Potential ◽

Human Airways

Many studies that demonstrate an increase in airway smooth muscle in asthmatic patients rely on the assumption that bronchial internal perimeter ( Pi) or basement membrane perimeter ( Pbm) is a constant, i.e., not affected by fixation pressure or the degree of smooth muscle shortening. Because it is the basement membrane that has been purported to be the indistensible structure, this study examines the assumption that Pbm is not affected by fixation pressure. Pbm was determined for the same human airway segment ( n = 12) fixed at distending pressures of 0 cmH2O and 21 cmH2O in the absence of smooth muscle tone. Pbm for the segment fixed at 0 cmH2O was determined morphometrically, and the Pbm for the same segment, had the segment been fixed at 21 cmH2O, was predicted from knowing the luminal volume and length of the airway when distended to 21 cmH2O (organ bath-derived Pi). To ensure an accurate transformation of the organ bath-derived Pi value to a morphometry-derived Pbm value, had the segment been fixed at 21 cmH2O, the relationship between organ bath-derived Pi and morphometry-derived Pbm was determined for five different bronchial segments distended to 21 cmH2O and fixed at 21 cmH2O ( r2 = 0.99, P < 0.0001). Mean Pbm for bronchial segments fixed at 0 cmH2O was 9.4 ± 0.4 mm, whereas mean predicted Pbm, had the segments been fixed at 21 cmH2O, was 14.1 ± 0.5 mm ( P < 0.0001). This indicates that Pbm is not a constant when isolated airway segments without smooth muscle tone are fixed distended to 21 cmH2O. The implication of these results is that the increase in smooth muscle mass in asthma may have been overestimated in some previous studies. Therefore, further studies are required to examine the potential artifact using whole lungs with and without abolition of airway smooth muscle tone and/or inflation.

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Sympathetic nerve-dependent regulation of mucosal vascular tone modifies airway smooth muscle reactivity

Journal of Applied Physiology ◽

10.1152/japplphysiol.00632.2010 ◽

2010 ◽

Vol 109 (5) ◽

pp. 1292-1300 ◽

Cited By ~ 17

Author(s):

Stuart B. Mazzone ◽

Lina H. K. Lim ◽

Elizabeth M. Wagner ◽

Nanako Mori ◽

Brendan J. Canning

Keyword(s):

Blood Flow ◽

Smooth Muscle ◽

Airway Smooth Muscle ◽

Vascular Function ◽

Adrenergic Receptor ◽

Muscle Tone ◽

Mucosal Blood Flow ◽

Nerve Fibers ◽

Neurokinin A

The airways contain a dense subepithelial microvascular plexus that is involved in the supply and clearance of substances to and from the airway wall. We set out to test the hypothesis that airway smooth muscle reactivity to bronchoconstricting agents may be dependent on airway mucosal blood flow. Immunohistochemical staining identified vasoconstrictor and vasodilator nerve fibers associated with subepithelial blood vessels in the guinea pig airways. Intravital microscopy of the tracheal mucosal microvasculature in anesthetized guinea pigs revealed that blockade of α-adrenergic receptors increased baseline arteriole diameter by ∼40%, whereas the α-adrenergic receptor agonist phenylephrine produced a modest (5%) vasoconstriction in excess of the baseline tone. In subsequent in vivo experiments, tracheal contractions evoked by topically applied histamine were significantly reduced ( P < 0.05) and enhanced by α-adrenergic receptor blockade and activation, respectively. α-Adrenergic ligands produced similar significant ( P < 0.05) effects on airway smooth muscle contractions evoked by topically administered capsaicin, intravenously administered neurokinin A, inhaled histamine, and topically administered antigen in sensitized animals. These responses were independent of any direct effect of α-adrenergic ligands on the airway smooth muscle tone. The data suggest that changes in blood flow in the vessels supplying the airways regulate the reactivity of the underlying airway smooth muscle to locally released and exogenously administered agents by regulating their clearance. We speculate that changes in mucosal vascular function or changes in neuronal regulation of the airway vasculature may contribute to airways responsiveness in disease.

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