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Sorensen DW, Injeti ER, Mejia-Aguilar L, Williams JM, Pearce WJ. Postnatal development alters functional compartmentalization of myosin light chain kinase in ovine carotid arteries. Am J Physiol Regul Integr Comp Physiol 2021; 321:R441-R453. [PMID: 34318702 PMCID: PMC8530762 DOI: 10.1152/ajpregu.00293.2020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The rate-limiting enzyme for vascular contraction, myosin light chain kinase (MLCK), phosphorylates regulatory myosin light chain (MLC20) at rates that appear faster despite lower MLCK abundance in fetal compared with adult arteries. This study explores the hypothesis that greater apparent tissue activity of MLCK in fetal arteries is due to age-dependent differences in intracellular distribution of MLCK in relation to MLC20. Under optimal conditions, common carotid artery homogenates from nonpregnant adult female sheep and near-term fetuses exhibited similar values of Vmax and Km for MLCK. A custom-designed, computer-controlled apparatus enabled electrical stimulation and high-speed freezing of arterial segments at exactly 0, 1, 2, and 3 s, calculation of in situ rates of MLC20 phosphorylation, and measurement of time-dependent colocalization between MLCK and MLC20. The in situ rate of MLC20 phosphorylation divided by total MLCK abundance averaged to values 147% greater in fetal (1.06 ± 0.28) than adult (0.43 ± 0.08) arteries, which corresponded, respectively, to 43 ± 10% and 31 ± 3% of the Vmax values measured in homogenates. Confocal colocalization analysis revealed in fetal and adult arteries that 33 ± 6% and 20 ± 5% of total MLCK colocalized with pMLC20, and that MLCK activation was greater in periluminal than periadventitial regions over the time course of electrical stimulation in both age groups. Together, these results demonstrate that the catalytic activity of MLCK is similar in fetal and adult arteries, but that the fraction of total MLCK in the functional compartment involved in contraction is significantly greater in fetal than adult arteries.
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Affiliation(s)
- Dane W Sorensen
- Division of Physiology, Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, California
| | - Elisha R Injeti
- Department of Pharmaceutical Sciences, Cedarville University School of Pharmacy, Cedarville, Ohio
| | - Luisa Mejia-Aguilar
- Division of Physiology, Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, California
| | - James M Williams
- Division of Physiology, Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, California
| | - William J Pearce
- Division of Physiology, Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, California
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2
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Jang JH, Panariti A, O’Sullivan MJ, Pyrch M, Wong C, Lauzon AM, Martin JG. Characterization of cystic fibrosis airway smooth muscle cell proliferative and contractile activities. Am J Physiol Lung Cell Mol Physiol 2019; 317:L690-L701. [DOI: 10.1152/ajplung.00090.2019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Cystic fibrosis (CF) is a genetic disease that causes multiple airway abnormalities. Two major respiratory consequences of CF are airway hyperresponsiveness (AHR) and airway remodeling. Airway smooth muscle (ASM) is hypothesized to be responsible for the airway dysfunction, since their thickening is involved in remodeling, and excessive contraction by the ASM may cause AHR. It is unclear whether the ASM is intrinsically altered to favor increased contractility or proliferation or if microenvironmental influences induce pathological behavior in vivo. In this study, we examined the contractile and proliferative properties of ASM cells isolated from healthy donor and CF transplant lungs. Assays of proliferation showed that CF ASM proliferates at a higher rate than healthy cells. Through calcium analysis, no differences in contractile activation in response to histamine were found. However, CF ASM cells lagged in their reuptake of calcium in the sarcoplasmic reticulum. The combination CFTR corrector and potentiator, VX-809/770, used to restore CFTR function in CF ASM, resulted in a reduction in proliferation and in a normalization of calcium reuptake kinetics. These results show that impaired CFTR function in ASM cells causes intrinsic changes in their proliferative and contractile properties.
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Affiliation(s)
- Joyce Hojin Jang
- Meakins-Christie Laboratories, McGill University Health Center and McGill University, Montreal, Quebec, Canada
- Department of Medicine, McGill University, Montreal, Quebec, Canada
| | - Alice Panariti
- Meakins-Christie Laboratories, McGill University Health Center and McGill University, Montreal, Quebec, Canada
| | - Michael J. O’Sullivan
- Meakins-Christie Laboratories, McGill University Health Center and McGill University, Montreal, Quebec, Canada
| | - Melissa Pyrch
- Meakins-Christie Laboratories, McGill University Health Center and McGill University, Montreal, Quebec, Canada
| | - Chris Wong
- Meakins-Christie Laboratories, McGill University Health Center and McGill University, Montreal, Quebec, Canada
| | - Anne-Marie Lauzon
- Meakins-Christie Laboratories, McGill University Health Center and McGill University, Montreal, Quebec, Canada
- Department of Medicine, McGill University, Montreal, Quebec, Canada
| | - James G. Martin
- Meakins-Christie Laboratories, McGill University Health Center and McGill University, Montreal, Quebec, Canada
- Department of Medicine, McGill University, Montreal, Quebec, Canada
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Chitano P, Wang L, Tin GYY, Ikebe M, Paré PD, Seow CY. Smooth muscle function and myosin polymerization. J Cell Sci 2017; 130:2468-2480. [DOI: 10.1242/jcs.202812] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 06/01/2017] [Indexed: 01/28/2023] Open
Abstract
Smooth muscle is able to function over a much broader length range than striated muscle. The ability to maintain contractility after a large length change is thought to be due to an adaptive process involving restructuring of the contractile apparatus to maximize overlap between the contractile filaments. The molecular mechanism for the length-adaptive behavior is largely unknown. In smooth muscle adapted to different lengths we quantified myosin monomers, basal and activation-induced myosin light chain (MLC) phosphorylation, shortening-velocity, power-output and active force. The muscle was able to generate a constant maximal force over a 2-fold length range when it was allowed to go through isometric contraction/relaxation cycles after each length change (length adaptation). In the relaxed state myosin monomer concentration and basal MLC phosphorylation decreased linearly, while in the activated state activation-induced MLC phosphorylation and shortening-velocity/power-output increased linearly with muscle length. The results suggest that recruitment of myosin monomers and oligomers into the actin filament lattice (where they form force-generating filaments) occurs during muscle adaptation to longer length with the opposite occurring during adaptation to shorter length.
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Affiliation(s)
- Pasquale Chitano
- Centre for Heart Lung Innovation - St. Paul's Hospital, University of British Columbia, Vancouver, BC, Canada
| | - Lu Wang
- Respiratory Division, Department of Medicine, University of British Columbia, Vancouver, BC, Canada
- Centre for Heart Lung Innovation - St. Paul's Hospital, University of British Columbia, Vancouver, BC, Canada
| | - Gabrielle Y. Y. Tin
- Centre for Heart Lung Innovation - St. Paul's Hospital, University of British Columbia, Vancouver, BC, Canada
| | - Mitsuo Ikebe
- Department of Cellular and Molecular Biology, University of Texas Health Science Center, Tyler, Texas, USA
| | - Peter D. Paré
- Respiratory Division, Department of Medicine, University of British Columbia, Vancouver, BC, Canada
- Centre for Heart Lung Innovation - St. Paul's Hospital, University of British Columbia, Vancouver, BC, Canada
| | - Chun Y. Seow
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, BC, Canada
- Centre for Heart Lung Innovation - St. Paul's Hospital, University of British Columbia, Vancouver, BC, Canada
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Wang L, Paré PD, Seow CY. The importance of complete tissue homogenization for accurate stoichiometric measurement of myosin light chain phosphorylation in airway smooth muscle. Can J Physiol Pharmacol 2014; 93:155-62. [PMID: 25494914 DOI: 10.1139/cjpp-2014-0357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
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.
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Affiliation(s)
- Lu Wang
- a Respiratory Division, Department of Medicine, Vancouver, BC V5Z 1M9, Canada
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Chitano P, Wang L, Degan S, Worthington CL, Pozzato V, Hussaini SH, Turner WC, Dorscheid DR, Murphy TM. Ovalbumin sensitization of guinea pig at birth prevents the ontogenetic decrease in airway smooth muscle responsiveness. Physiol Rep 2014; 2:2/12/e12241. [PMID: 25501429 PMCID: PMC4332219 DOI: 10.14814/phy2.12241] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Airway smooth muscle (ASM) displays a hyperresponsive phenotype at young age and becomes less responsive in adulthood. We hypothesized that allergic sensitization, which causes ASM hyperresponsiveness and typically occurs early in life, prevents the ontogenetic loss of the ASM hyperresponsive phenotype. We therefore studied whether neonatal allergic sensitization, not followed by later allergen challenges, alters the ontogenesis of ASM properties. We neonatally sensitized guinea pigs to ovalbumin and studied them at 1 week, 3 weeks, and 3 months (adult). A Schultz‐Dale response in isolated tracheal rings confirmed sensitization. The occurrence of inflammation was evaluated in the blood and in the submucosa of large airways. We assessed ASM function in tracheal strips as ability to produce force and shortening. ASM content of vimentin was also studied. A Schultz‐Dale response was observed in all 3‐week or older sensitized animals. A mild inflammatory process was characterized by eosinophilia in the blood and in the airway submucosa. Early life sensitization had no effect on ASM force generation, but prevented the ontogenetic decline of shortening velocity and the increase in resistance to shortening. Vimentin increased with age in control but not in sensitized animals. Allergic sensitization at birth without subsequent allergen exposures is sufficient to prevent normal ASM ontogenesis, inducing persistence to adulthood of an ASM hyperresponsive phenotype. Airway smooth muscle (ASM) displays a hyperresponsive phenotype at young age and becomes less responsive in adulthood. In this study, we found that allergic sensitization at birth without subsequent allergen exposures is sufficient to prevent normal ASM ontogenesis, inducing persistence to adulthood of an ASM hyperresponsive phenotype.
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Affiliation(s)
- Pasquale Chitano
- Division of Pediatric Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina James Hogg Research Centre, Institute for Heart and Lung Innovation and Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Lu Wang
- Division of Pediatric Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina James Hogg Research Centre, Institute for Heart and Lung Innovation and Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Simone Degan
- Duke Center for Molecular and Biomolecular Imaging, Duke University Medical Center, Durham, North Carolina Duke Department of Radiology, Duke University Medical Center, Durham, North Carolina
| | - Charles L Worthington
- Division of Pediatric Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina
| | - Valeria Pozzato
- Division of Pediatric Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina
| | - Syed H Hussaini
- Division of Pediatric Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina
| | - Wesley C Turner
- Division of Pediatric Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina
| | - Delbert R Dorscheid
- James Hogg Research Centre, Institute for Heart and Lung Innovation and Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - Thomas M Murphy
- Division of Pediatric Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina
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Nicotine stimulates nerve growth factor in lung fibroblasts through an NFκB-dependent mechanism. PLoS One 2014; 9:e109602. [PMID: 25296021 PMCID: PMC4190411 DOI: 10.1371/journal.pone.0109602] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Accepted: 09/12/2014] [Indexed: 11/19/2022] Open
Abstract
RATIONALE Airway hyperresponsiveness (AHR) is classically found in asthma, and persistent AHR is associated with poor asthma control. Although airway smooth muscle (ASM) cells play a critical pathophysiologic role in AHR, the paracrine contributions of surrounding cells such as fibroblasts to the contractile phenotype of ASM cells have not been examined fully. This study addresses the hypothesis that nicotine promotes a contractile ASM cell phenotype by stimulating fibroblasts to increase nerve growth factor (NGF) secretion into the environment. METHODS Primary lung fibroblasts isolated from wild type and α7 nicotinic acetylcholine receptor (α7 nAChR) deficient mice were treated with nicotine (50 µg/ml) in vitro for 72 hours. NGF levels were measured in culture media and in bronchoalveolar lavage (BAL) fluid from asthmatic, smoking and non-smoking subjects by ELISA. The role of the NFκB pathway in nicotine-induced NGF expression was investigated by measuring NFκB nuclear translocation, transcriptional activity, chromatin immunoprecipitation assays, and si-p65 NFκB knockdown. The ability of nicotine to stimulate a fibroblast-mediated, contractile ASM cell phenotype was confirmed by examining expression of contractile proteins in ASM cells cultured with fibroblast-conditioned media or BAL fluid. RESULTS NGF levels were elevated in the bronchoalveolar lavage fluid of nicotine-exposed mice, current smokers, and asthmatic children. Nicotine increased NGF secretion in lung fibroblasts in vitro in a dose-dependent manner and stimulated NFκB nuclear translocation, p65 binding to the NGF promoter, and NFκB transcriptional activity. These responses were attenuated in α7 nAChR deficient fibroblasts and in wild type fibroblasts following NFκB inhibition. Nicotine-treated, fibroblast-conditioned media increased expression of contractile proteins in ASM cells. CONCLUSION Nicotine stimulates NGF release by lung fibroblasts through α7 nAChR and NFκB dependent pathways. These novel findings suggest that the nicotine-α7 nAChR-NFκB- NGF axis may provide novel therapeutic targets to attenuate tobacco smoke-induced AHR.
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Chitano P. Models to understand contractile function in the airways. Pulm Pharmacol Ther 2011; 24:444-51. [PMID: 21511049 DOI: 10.1016/j.pupt.2011.04.028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Revised: 04/04/2011] [Accepted: 04/07/2011] [Indexed: 11/25/2022]
Abstract
Although the role of contractile function in the airways is controversial, there is general consensus on the importance of airway smooth muscle (ASM) as a therapeutic target for diseases characterized by airway obstruction, such as asthma or chronic obstructive pulmonary disease. Indeed, the use of bronchodilators to relax ASM is the most common and effective practice to treat airflow obstruction. Excessive pathologic bronchoconstriction may originate from primary alterations of ASM mechanical function and/or from the effects exerted on ASM function by disease processes, such as inflammation and remodeling. An in depth knowledge of the potentially multiple mechanisms that distinctively regulate primary and secondary alterations in ASM contractile function would be essential for the development of new therapeutic approaches aimed at preventing the occurrence or reducing the severity of bronchoconstriction. The present review discusses studies that have addressed the mechanisms of altered ASM contractile function in models of airway hyperresponsiveness. Although not comprehensively, in the present review, animal models of intrinsic airway hyperresponsiveness, normal ontogenesis, and allergic sensitization are analyzed in the attempt to summarize the current knowledge on regulatory mechanisms of ASM contractile function in health and disease. Studies in human ASM and the need for additional models to understand contractile function in the airways are also discussed.
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Affiliation(s)
- Pasquale Chitano
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, NC 27710, USA.
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Injeti ER, Sandoval RJ, Williams JM, Smolensky AV, Ford LE, Pearce WJ. Maximal stimulation-induced in situ myosin light chain kinase activity is upregulated in fetal compared with adult ovine carotid arteries. Am J Physiol Heart Circ Physiol 2008; 295:H2289-98. [PMID: 18835918 DOI: 10.1152/ajpheart.00606.2008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Postnatal decreases in vascular reactivity involve decreases in the thick filament component of myofilament calcium sensitivity, which is measured as the relationship between cytosolic calcium concentration and myosin light chain (MLC20) phosphorylation. The present study tests the hypothesis that downregulation of thick filament reactivity is due to downregulation of myosin light chain kinase (MLCK) activity in adult compared with fetal arteries. Total MLCK activity, calculated as %MLC20 phosphorylated per second in intact arteries during optimal inhibition of myosin light chain phosphatase activity, was significantly less in adult (6.56+/-0.29%) than in fetal preparations (7.39+/-0.53%). In situ MLC20 concentrations (microM) in adult (198+/-28) and fetal arteries (236+/-44) did not differ significantly. In situ MLCK concentrations (microM), however, were significantly greater in adult (8.21+/-0.59) than in fetal arteries (1.83+/-0.13). In situ MLCK activities (ng MLC20 phosphorylated.s(-1).ng MLCK(-1)) were significantly less in adult (0.26+/-0.01) than in fetal arteries (1.52+/-0.11). In contrast, MLCK activities in adult (15.8+/-1.5) and fetal artery homogenates (17.3+/-1.3) were not significantly different. When in situ fractional activation was calculated, adult values (1.72+/-0.17%) were significantly less than fetal values (9.08+/-0.83%). Together, these results indicate that decreased thick filament reactivity in adult compared with fetal ovine carotid arteries is due at least in part to greater MLCK activity in fetal arteries, which in turn cannot be explained by differences in MLCK, MLC20, or calmodulin concentrations. Instead, this difference appears to involve age-related differences in fractional activation of the MLCK enzyme.
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Affiliation(s)
- Elisha R Injeti
- Center for Perinatal Biology, Loma Linda University School of Medicine, Loma Linda, CA 92354, USA
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Chitano P, Wang L, Murphy TM. Three paradigms of airway smooth muscle hyperresponsiveness in young guinea pigs. Can J Physiol Pharmacol 2007; 85:715-26. [PMID: 17823635 PMCID: PMC2527444 DOI: 10.1139/y07-063] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Evidence for contributions of airway smooth muscle (ASM) to the hyperresponsiveness of newborn and juvenile airways continues to accumulate. In our laboratory, 3 novel paradigms of hyperresponsiveness of newborn and young ASM have recently emerged using a guinea pig model of maturation in 3 age groups: 1 week (newborn), 3 weeks (juvenile), and 2-3 months (adult). The first paradigm includes evidence for a natural decline after newborn and juvenile life of the velocity of ASM shortening associated with a decrease in regulatory myosin light chain phosphorylation and a parallel decline in the content of myosin light chain kinase. Associated with the decrease in ASM shortening with age is an increase in the internal resistance to shortening. Dynamic stiffness is shown to relate inversely to the expression of myosin light chain kinase. This suggests that developmental changes in shortening relate inversely to the stiffness of the ASM early in shortening, suggesting a dynamic role for the cytoskeleton in facilitating and opposing ASM shortening. This relationship can be approximated as (dP/dt)max approximately (dP/dL)passive x (dL/dt)max (the maximal rate of increase of active stress generation approximately to the passive stiffness x the maximal shortening velocity). The second paradigm demonstrates that newborn ASM, unlike that in adults, does not relax during prolonged electric field stimulation. The impaired relaxation is related to changes in prostanoid synthesis and acetylcholinesterase function. The third paradigm demonstrates that, whereas oscillatory strain serves to transiently relax adult ASM, in newborns it induces (after the initial relaxation) a sustained potentiation of active stress. This is related to developmental changes in the prostanoid release. Together, these paradigms demonstrate that ASM contributes by multiple mechanisms to the natural hyperresponsiveness of newborn and juvenile airways. Future studies will elaborate the mechanisms and extend these paradigms to ASM hyperresponsiveness following sensitization in early life.
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Affiliation(s)
- Pasquale Chitano
- Division of Pediatric Pulmonary and Sleep Medicine and the Neonatal Perinatal Research Institute, Room 302, Bell Building, Duke University, Durham, NC 27710, USA.
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Chitano P, Wang L, Murphy TM. Mechanisms of airway smooth muscle relaxation during maturation. Can J Physiol Pharmacol 2006; 83:833-40. [PMID: 16333354 DOI: 10.1139/y05-056] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Greater airway responsiveness in healthy juveniles is considered a factor in the higher asthma prevalence at a young age compared with adults. We have developed a guinea pig maturational model that utilizes tracheal strips from 1-week-, 3-week-, and 3-month-old guinea pigs to study the role of airway smooth muscle (ASM) in juvenile airway hyperresponsiveness. Because a reduced ability of ASM to spontaneously relax may contribute to airway hyperresponsiveness by maintaining bronchospasm and thus high airway resistance, we have employed this model to study ASM spontaneous relaxation during electrical field stimulation (EFS). Since relaxation during EFS had been neither described nor quantified during maturation, we developed new indices that allowed an appropriate comparison of the relaxing response from strips of different age animals. Using these indices we found that, whereas strips from adult animals relax to a level of tension similar to that found in the absence of stimulation, this ability to spontaneously relax is essentially absent in trachealis from infant animals. These results confirmed that maturation of ASM relaxation may play a role in juvenile airway hyperresponsiveness and that our maturational model is suitable to study the mechanisms regulating spontaneous relaxation in physiological conditions. We investigated the role of prostanoids in ASM relaxation and showed that cyclooxygenase inhibition increases relaxation in infant ASM to levels similar to adults. These results suggest that prostanoids regulate the ability of ASM to spontaneously relax, i.e., they reduce relaxation. We have produced preliminary data suggesting a maturational change in the level of prostanoids. Moreover, the possible action of acetylcholinesterase on maturation of ASM relaxation is discussed here on the basis of a preliminary study. We suggest that impairment of ASM relaxation likely contributes to increased airway responsiveness.
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Affiliation(s)
- Pasquale Chitano
- Department of Pediatrics, Duke University Medical Center, Durham, NC 27710, USA.
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