Increase in passive stiffness at reduced airway smooth muscle length: potential impact on airway responsiveness

2010 ◽  
Vol 298 (3) ◽  
pp. L277-L287 ◽  
Author(s):  
Ynuk Bossé ◽  
Dennis Solomon ◽  
Leslie Y. M. Chin ◽  
Kevin Lian ◽  
Peter D. Paré ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Kinase Inhibitor ◽  
Rho Kinase ◽  
Muscle Length ◽  
Passive Stiffness ◽  
Tidal Breathing ◽  
Reference Length ◽  
Length Reduction

The amplitude of strain in airway smooth muscle (ASM) produced by oscillatory perturbations such as tidal breathing or deep inspiration (DI) influences the force loss in the muscle and is therefore a key determinant of the bronchoprotective and bronchodilatory effects of these breathing maneuvers. The stiffness of unstimulated ASM (passive stiffness) directly influences the amplitude of strain. The nature of the passive stiffness is, however, not clear. In this study, we measured the passive stiffness of ovine ASM at different muscle lengths (relative to in situ length, which was used as a reference length, Lref) and states of adaptation to gain insights into the origin of this muscle property. The results showed that the passive stiffness was relatively independent of muscle length, possessing a constant plateau value over a length range from 0.62 to 1.25 Lref. Following a halving of ASM length, passive stiffness decreased substantially (by 71%) but redeveloped over time (∼30 min) at the shorter length to reach 65% of the stiffness value at Lref, provided that the muscle was stimulated to contract at least once over a ∼30-min period. The redevelopment and maintenance of passive stiffness were dependent on the presence of Ca2+ but unaffected by latrunculin B, an inhibitor of actin filament polymerization. The maintenance of passive stiffness was also not affected by blocking myosin cross-bridge cycling using a myosin light chain kinase inhibitor or by blocking the Rho-Rho kinase (RhoK) pathway using a RhoK inhibitor. Our results suggest that the passive stiffness of ASM is labile and capable of redevelopment following length reduction. Redevelopment and maintenance of passive stiffness following muscle shortening could contribute to airway hyperresponsiveness by attenuating the airway wall strain induced by tidal breathing and DI.

Regulatable stiffness in relaxed airway smooth muscle: a target for asthma treatment?

2012 ◽  
Vol 112 (3) ◽  
pp. 337-346 ◽  
Author(s):  
Abdul Raqeeb ◽  
Yuekan Jiao ◽  
Harley T. Syyong ◽  
Peter D. Paré ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Light Chain ◽  
Myosin Light Chain ◽  
Kinase Inhibitor ◽  
Rho Kinase ◽  
Muscle Layer ◽  
Radial Force ◽  
Calcium Entry Blocker ◽  
Passive Stiffness

The airway smooth muscle (ASM) layer within the airway wall modulates airway diameter and distensibility. Even in the relaxed state, the ASM layer possesses finite stiffness and limits the extent of airway distension by the radial force generated by parenchymal tethers and transmural pressure. Airway stiffness has often been attributed to passive elements, such as the extracellular matrix in the lamina reticularis, adventitia, and the smooth muscle layer that cannot be rapidly modulated by drug intervention such as ASM relaxation by β-agonists. In this study, we describe a calcium-sensitive component of ASM stiffness mediated through the Rho-kinase signaling pathway. The stiffness of ovine tracheal smooth muscle was assessed in the relaxed state under the following conditions: 1) in physiological saline solution (Krebs solution) with normal calcium concentration; 2) in calcium-free Krebs with 2 mM EGTA; 3) in Krebs with calcium entry blocker (SKF-96365); 4) in Krebs with myosin light chain kinase inhibitor (ML-7); and 5) in Krebs with Rho-kinase inhibitor (Y-27632). It was found that a substantial portion of the passive stiffness could be abolished when intracellular calcium was removed; this calcium-sensitive stiffness appeared to stem from intracellular source and was not sensitive to ML-7 inhibition of myosin light chain phosphorylation, but was sensitive to Y-27632 inhibition of Rho kinase. The results suggest that airway stiffness can be readily modulated by targeting the calcium-sensitive component of the passive stiffness within the muscle layer.

Relaxation of activated airway smooth muscle: relative potency of isoproterenol vs. tidal stretch

2001 ◽  
Vol 90 (6) ◽  
pp. 2306-2310 ◽  
Author(s):  
Alison Gump ◽  
Laura Haughney ◽  
Jeffrey Fredberg
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Signal Transduction Pathway ◽  
Muscle Length ◽  
Active Force ◽  
Tidal Breathing ◽  
First Line ◽  
Relaxation Effects ◽  
High Concentrations ◽  
Multiplicative Effects

Both isoproterenol and tidal fluctuations of muscle length inhibit active force development in activated airway smooth muscle. In this study, we show that length fluctuations in the range of amplitudes expected during quiet tidal breathing produce force inhibition that is equipotent with high concentrations of isoproterenol. Active force fell to 50% of its isometric value when the amplitude of the tidal stretch was 4% of muscle length. The relaxing effects of length fluctuations were insensitive to the specific contractile agonist, suggesting that the mechanism of action is largely independent of the particular signal transduction pathway and lies instead at the level of bridge dynamics. This idea is reinforced by the results of combining the relaxation effects of tidal fluctuations with those produced by isoproterenol at all but the highest concentrations studied (10−5 M). Such a combination produces multiplicative effects, indicating largely separate modes of action. These observations suggest that the tidal muscle stretches that are attendant to spontaneous breathing comprise the first line of defense against bronchospasm and that tidal muscle stretches may be the most important of all known bronchodilating agencies.

Latrunculin B increases force fluctuation-induced relengthening of ACh-contracted, isotonically shortened canine tracheal smooth muscle

2005 ◽  
Vol 98 (2) ◽  
pp. 489-497 ◽  
Author(s):  
M. L. Dowell ◽  
O. J. Lakser ◽  
W. T. Gerthoffer ◽  
J. J. Fredberg ◽  
G. L. Stelmack ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Actin Filament ◽  
Isometric Force ◽  
Muscle Length ◽  
Tracheal Smooth Muscle ◽  
Filament Length ◽  
Latrunculin B ◽  
Force Fluctuation ◽  
Reference Length

We hypothesized that differences in actin filament length could influence force fluctuation-induced relengthening (FFIR) of contracted airway smooth muscle and tested this hypothesis as follows. One-hundred micromolar ACh-stimulated canine tracheal smooth muscle (TSM) strips set at optimal reference length ( Lref) were allowed to shorten against 32% maximal isometric force (Fmax) steady preload, after which force oscillations of ±16% Fmax were superimposed. Strips relengthened during force oscillations. We measured hysteresivity and calculated FFIR as the difference between muscle length before and after 20-min imposed force oscillations. Strips were relaxed by ACh removal and treated for 1 h with 30 nM latrunculin B (sequesters G-actin and promotes depolymerization) or 500 nM jasplakinolide (stabilizes actin filaments and opposes depolymerization). A second isotonic contraction protocol was then performed; FFIR and hysteresivity were again measured. Latrunculin B increased FFIR by 92.2 ± 27.6% Lref and hysteresivity by 31.8 ± 13.5% vs. pretreatment values. In contrast, jasplakinolide had little influence on relengthening by itself; neither FFIR nor hysteresivity was significantly affected. However, when jasplakinolide-treated tissues were then incubated with latrunculin B in the continued presence of jasplakinolide for 1 more h and a third contraction protocol performed, latrunculin B no longer substantially enhanced TSM relengthening. In TSM treated with latrunculin B + jasplakinolide, FFIR increased by only 3.03 ± 5.2% Lref and hysteresivity by 4.14 ± 4.9% compared with its first (pre-jasplakinolide or latrunculin B) value. These results suggest that actin filament length, in part, determines the relengthening of contracted airway smooth muscle.

Hyperoxic conditions inhibit airway smooth muscle myosin phosphatase in rat pups

2007 ◽  
Vol 292 (1) ◽  
pp. L68-L73 ◽  
Author(s):  
Paul G. Smith ◽  
Albana Dreshaj ◽  
Subhendu Chaudhuri ◽  
Baran M. Onder ◽  
Maroun J. Mhanna ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Kinase Inhibitor ◽  
Rho Kinase ◽  
Electrical Field Stimulation ◽  
Smooth Muscle Myosin ◽  
Postnatal Life ◽  
Myosin Phosphatase ◽  
Rat Pups ◽  
Muscle Myosin

Exposure of rat pups to 100% oxygen is a model for studying neonatal lung injury. Airway reactivity is increased in this model, in part due to impaired airway smooth muscle (ASM) relaxation. We compared biochemical determinants of ASM contractility in rat pups exposed to 100% oxygen for 7 days vs. littermates raised in room air. The baseline quantities of ASM contractile proteins, extent of phosphorylation of the 20-kDa myosin regulatory light chain (LC20), and amount of the myosin-binding subunit of smooth muscle myosin phosphatase (MYPT) were all comparable between the two groups. Bethanechol-induced contraction increased the extent of phosphorylation of both LC20 and MYPT in the hyperoxic group (45% and 70% over control, respectively). Relaxation after electrical field stimulation demonstrated greater phosphorylation of both LC20 and MYPT in the hyperoxic group compared with controls (67% and 84%, respectively). To determine if hyperoxia induced changes in the isoforms of MYPT, isoform expression was also compared but differences were not found. To determine potential mechanisms whereby MYPT phosphorylation was increased by hyperoxia, separate tracheas were treated with the Rho kinase inhibitor Y-27632. This treatment completely eliminated differences in MYPT phosphorylation between the groups. Because phosphorylation of MYPT impairs the phosphatase activity of myosin phosphatase, these data suggest that hyperoxic conditioning during early postnatal life impairs relaxation through prolonging LC20 phosphorylation. This mechanism might contribute to increased ASM reactivity seen in bronchopulmonary dysplasia.

5-Oxo-ETE regulates tone of guinea pig airway smooth muscle via activation of Ca2+ pools and Rho-kinase pathway

2004 ◽  
Vol 287 (4) ◽  
pp. L631-L640 ◽  
Author(s):  
Frederic Mercier ◽  
Caroline Morin ◽  
Martin Cloutier ◽  
Sonia Proteau ◽  
Joshua Rokach ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Guinea Pig ◽  
Airway Smooth Muscle ◽  
Kinase Inhibitor ◽  
Rho Kinase ◽  
Eicosatetraenoic Acid ◽  
Chlorobenzoic Acid ◽  
Tp Receptor ◽  
Lower Amplitude ◽  
Inotropic Responses

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a proinflammatory mediator, but its effects on airway smooth muscle (ASM) have never been assessed. Tension measurements performed on guinea pig ASM showed that 5-oxo-ETE induced sustained concentration-dependent positive inotropic responses (EC50 = 0.89 μM) of somewhat lower amplitude than those induced by carbamylcholine and the thromboxane A2 (TXA2) agonist U-46619. Transient inotropic responses to 5-oxo-ETE were recorded in Ca2+-free medium, suggesting mobilization of intracellular Ca2+. Meanwhile, the sustained contraction, which required Ca2+ entry, was partially blocked by 1 μM nifedipine (an L-type Ca2+ channel blocker) but relatively insensitive to 100 μM Gd3+. The 5-oxo-ETE responses were also inhibited by indomethacin and SC-560 [a cyclooxygenase (COX-1) inhibitor] pretreatments but not by NS-398 (a selective COX-2 inhibitor). The contractile effects of 5-oxo-ETE on ASM were inhibited by the selective TXA2 receptor (TP receptor) antagonist SQ-29548 (−75%) and by 2-(p-amylcinnamoyl) amino-4-chlorobenzoic acid pretreatment, a phospholipase A2 inhibitor (−66%), suggesting that the major part of its effect is mediated by the release of TXA2. ASM responses to 5-oxo-ETE were also blocked by the Rho-kinase inhibitor Y-27632, which also partially inhibited the response to the TP receptor agonist U-46619, suggesting that the contractile response is due in part to Ca2+ sensitization of ASM cell myofilaments.

Insulin increases the expression of contractile phenotypic markers in airway smooth muscle

2007 ◽  
Vol 293 (1) ◽  
pp. C429-C439 ◽  
Author(s):  
Dedmer Schaafsma ◽  
Karol D. McNeill ◽  
Gerald L. Stelmack ◽  
Reinoud Gosens ◽  
Hoeke A. Baarsma ◽  
...  
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Cell Morphology ◽  
Kinase Inhibitor ◽  
Rho Kinase ◽  
Protein Accumulation ◽  
Mrna Levels ◽  
Phenotypic Markers ◽  
Serum Free ◽  
Contractile Phenotype

We have previously demonstrated that long-term exposure of bovine tracheal smooth muscle (BTSM) strips to insulin induces a functional hypercontractile phenotype. To elucidate molecular mechanisms by which insulin might induce maturation of contractile phenotype airway smooth muscle (ASM) cells, we investigated effects of insulin stimulation in serum-free primary BTSM cell cultures on protein accumulation of specific contractile phenotypic markers and on the abundance and stability of mRNA encoding these markers. In addition, we used microscopy to assess insulin effects on ASM cell morphology, phenotype, and induction of phosphatidylinositol (PI) 3-kinase signaling. It was demonstrated that protein and mRNA levels of smooth muscle-specific contractile phenotypic markers, including sm-myosin, are significantly increased after stimulation of cultured BTSM cells with insulin (1 μM) for 8 days compared with cells treated with serum-free media, whereas mRNA stability was unaffected. In addition, insulin treatment promoted the formation of large, elongate ASM cells, characterized by dramatic accumulation of contractile phenotype marker proteins and phosphorylated p70S6K (downstream target of PI 3-kinase associated with ASM maturation). Insulin effects on protein accumulation and cell morphology were abrogated by combined pretreatment with the Rho kinase inhibitor Y-27632 (1 μM) or the PI 3-kinase inhibitor LY-294002 (10 μM), indicating that insulin increases the expression of contractile phenotypic markers in BTSM in a Rho kinase- and PI 3-kinase-dependent fashion. In conclusion, insulin increases transcription and protein expression of contractile phenotypic markers in ASM. This could have important implications for the use of recently approved aerosolized insulin formulations in diabetes mellitus.

Length oscillation mimicking periodic individual deep inspirations during tidal breathing attenuates force recovery and adaptation in airway smooth muscle

2010 ◽  
Vol 109 (5) ◽  
pp. 1476-1482 ◽  
Author(s):  
Abdul Raqeeb ◽  
Dennis Solomon ◽  
Peter D. Paré ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Prolonged Exposure ◽  
Dynamic Environment ◽  
Muscle Length ◽  
Deep Inspiration ◽  
Tidal Breathing ◽  
Maximal Force ◽  
Force Recovery ◽  
Static Conditions

Airway smooth muscle (ASM) is able to generate maximal force under static conditions, and this isometric force can be maintained over a large length range due to length adaptation. The increased force at short muscle length could lead to excessive narrowing of the airways. Prolonged exposure of ASM to submaximal stimuli also increases the muscle's ability to generate force in a process called force adaptation. To date, the effects of length and force adaptation have only been demonstrated under static conditions. In the mechanically dynamic environment of the lung, ASM is constantly subjected to periodic stretches by the parenchyma due to tidal breathing and deep inspiration. It is not known whether force recovery due to muscle adaptation to a static environment could occur in a dynamic environment. In this study the effect of length oscillation mimicking tidal breathing and deep inspiration was examined. Force recovery after a length change was attenuated in the presence of length oscillation, except at very short lengths. Force adaptation was abolished by length oscillation. We conclude that in a healthy lung (with intact airway-parenchymal tethering) where airways are not allowed to narrow excessively, large stretches (associated with deep inspiration) may prevent the ability of the muscle to generate maximal force that would occur under static conditions irrespective of changes in mean length; mechanical perturbation on ASM due to tidal breathing and deep inspiration, therefore, is the first line of defense against excessive bronchoconstriction that may result from static length and force adaptation.

scholarly journals The contribution of Ca2+ signaling and Ca2+ sensitivity to the regulation of airway smooth muscle contraction is different in rats and mice

2009 ◽  
Vol 296 (6) ◽  
pp. L947-L958 ◽  
Author(s):  
Yan Bai ◽  
Michael J. Sanderson
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Laser Scanning ◽  
Kinase Inhibitor ◽  
Rho Kinase ◽  
Smooth Muscle Contraction ◽  
Laser Scanning Microscopy ◽  
Airway Smooth Muscle Cells ◽  
Similar Frequency ◽  
Sustained Contraction

To determine the relative contributions of Ca2+ signaling and Ca2+ sensitivity to the contractility of airway smooth muscle cells (SMCs), we compared the contractile responses of mouse and rat airways with the lung slice technique. Airway contraction was measured by monitoring changes in airway lumen area with phase-contrast microscopy, whereas changes in intracellular calcium concentration ([Ca2+]i) of the SMCs were recorded with laser scanning microscopy. In mice and rats, methacholine (MCh) or serotonin induced concentration-dependent airway contraction and Ca2+ oscillations in the SMCs. However, rat airways demonstrated greater contraction compared with mice, in response to agonist-induced Ca2+ oscillations of a similar frequency. Because this indicates that rat airway SMCs have a higher Ca2+ sensitivity compared with mice, we examined Ca2+ sensitivity with Ca2+-permeabilized airway SMCs in which the [Ca2+]i was experimentally controlled. In the absence of agonists, high [Ca2+]i induced a sustained contraction in rat airways but only a transient contraction in mouse airways. This sustained contraction of rat airways was relaxed by Y-23672, a Rho kinase inhibitor, but not affected by GF-109203X, a PKC inhibitor. The subsequent exposure of Ca2+-permeabilized airway SMCs, with high [Ca2+]i, to MCh elicited a further contraction of rat airways and initiated a sustained contraction of mouse airways, without changing the [Ca2+]i of the SMCs. Collectively, these results indicate that airway SMCs of rats have a substantially higher innate Ca2+ sensitivity than mice and that this strongly influences the transduction of the frequency of Ca2+ oscillations into the contractility of airway SMCs.

scholarly journals Mechanopharmacology and Synergistic Relaxation of Airway Smooth Muscle

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Lu Wang ◽  
Pasquale Chitano ◽  
Peter D. Paré ◽  
Chun Y. Seow
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Intracellular Signaling ◽  
Rho Kinase ◽  
Passive Stiffness ◽  
Rock Inhibitor ◽  
Drug Induced ◽  
Intracellular Signaling Pathways ◽  
Combination Treatments ◽  
Β2 Agonist

Asthmatic airways are stiffer than normal. We have shown that the cytoskeletal passive stiffness of airway smooth muscle (ASM) can be regulated by intracellular signaling pathways, especially those associated with Rho kinase (ROCK). We have also shown that an oscillatory strain reduces the passive stiffness of ASM and its ability to generate force. Here, we investigated the combined effect of inhibiting the ASM contraction with β2 agonist and decreasing the ASM cytoskeletal stiffness with ROCK inhibitor and/or force oscillation (FO) on the relaxation of contracted ASM. We hypothesize that the ASM relaxation can be synergistically enhanced by the combination of these interventions, because drug-induced softening of the cytoskeleton enhances the FO-induced relaxation and vice versa. Sheep tracheal strips were isotonically contracted to acetylcholine (3 × 10−5 M). At the plateau of shortening, β2 agonist salbutamol (10−7 M), ROCK inhibitor H1152 (10−7 M), and FO (square wave, 1 Hz, amplitude 6% maximal active force) were applied either alone or in combination. After adjusting for nonspecific time-dependent variation, relengthening by individual interventions with low-dose salbutamol or H1152, or small amplitude FO was not significantly different from zero. However, significant relengthening was observed in all combination treatments. The relengthening was greater than the mathematical sum of relengthening caused by individual treatments thereby demonstrating synergistic relaxation. The ASM stiffness did not change with salbutamol or H1152 treatments, but was lower with FO in combination with H1152. The results suggest that the mechanopharmacological treatment can be an effective therapy for asthma.

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