Contractility and Ca²⁺ Signaling of Smooth Muscle Cells in Different Generations of Mouse Airways

Abstract

The control and mechanisms of airway smooth muscle cell (SMC) contraction were investigated with a sequential series of lung slices from different generations of the same airway from the cardiac lobe of the mouse lung. Airway contraction was measured by monitoring the changes in airway lumen area with phase-contrast microscopy. Changes in intracellular calcium concentration of the SMCs were studied with a custom-built confocal or two-photon microscope. The distribution of the airway SMCs and the muscarinic Excessive contraction of airway smooth muscle cells (SMCs) is a major cause of airway narrowing in asthma. This change in the contractile function of SMCs frequently occurs secondarily to airway inflammation, which itself can contribute to increased resistance to airflow by thickening of the airway wall or mucus hypersecretion (1). Although inflammatory responses occur throughout the bronchial tree (2-4), the increased responsiveness and resistance due to airway narrowing appears to be more prevalent in the peripheral airways (1, 5-7). Therefore, to understand this localized reaction, it is important to determine if the contractile responses of SMCs vary in different sections of the respiratory tract and if this predisposes the peripheral airways to disease.Because of their small size and inaccessible location, the physiology of intact intrapulmonary airways has been difficult to study. As a result, comparative reports of the contractile responses in proximal and distal airways of different species are CLINICAL RELEVANCEThis study implies that the heterogeneity of airway contraction must be considered when the impact of the hyperreactivity of a diseased airway is evaluated. inconsistent (8-13). In general, the distal airways appeared more contractile than proximal airways and this difference may result from variations in the structure of the airway wall or the heterogeneity in the SMCs (13). However, a fundamental question is whether the contractility of individual SMC varies in different zones of the intrapulmonary airways. It has been shown that the magnitude of airway SMC contraction relates to the frequency of agonist-induced Ca 2ϩ oscillations within the SMCs (14, 15). Consequently, differences in the Ca 2ϩ signaling mechanism of SMC (e.g., agonist receptor distribution or type) could be responsible for the variation in contraction at different airway locations.The aim of this study was to compare the contractile responses of a range of sizes of intrapulmonary airways and correlate these responses with the intracellular Ca 2ϩ signaling of the SMCs. The observations of SMC contraction and Ca 2ϩ signaling in different airway locations have been made possible by the development of techniques to cut thin serial lung slices that can be observed with microscopy. With this approach, we found that methacholine (MCh) induced a concentration-dependent contraction of SMCs in each generation along the length of an airway through the cardiac lobe of a mouse lung. The greatest contractile response occurred in the mids...

Spatially resolved assessment of serotonin‐induced bronchoconstrictive responses in the rat lung using 3He ventilation MRI under spontaneous breathing conditions

“…In our study, no ventilation defect could be observed, but only homogeneous ventilation parameters decrease. This observation is in agreement with a more homogeneous distribution of serotonin receptors throughout the airway generations (18), whereas intravenous injection of methacholine predominantly elicits central airway obstruction (19) in relation to a higher presence of muscarinic M3 receptors in middle or proximal airways (18).…”

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

“…In previous experiments, we (2) established that the responsiveness of mouse airway SMCs varied in different airway generations and that the sensitivity of the relationship between contraction and Ca 2ϩ oscillations was decreased in larger airways. Because we have compared similar-sized airways from rat and mice, it is possible that the difference we observe between similar-sized mouse and rat airways is the result of a comparison of airways from different airway generations.…”

“…In addition, the idea that hyperresponsiveness is associated with a structural difference assumes that the underlying Ca 2ϩ -dependent signaling mechanisms in each SMC remains identical. However, our investigations have revealed that the extent of airway contraction varies at different airway locations and that this correlates with different frequencies of Ca 2ϩ oscillations within SMCs (2). Consequently, the focus of this study was to determine the importance of the contribution of the Ca 2ϩ signaling and Ca 2ϩ sensitivity to airway SMCs contractility by comparing these two processes in rats and mice.…”

“…We (2) found in our previous studies that airway responsiveness was related to location and that agonist-induced airway contraction was weaker in the more proximal and distal airways of mice compared with midrange airways. Most other studies have only examined airway SMCs isolated or cultured from the trachea or large central airways, therefore their relative responsiveness is not addressable.…”

Kinetics ofin vitrobronchoconstriction in an elastolytic mouse model of emphysema

“…BAI et al [21] have shown that the magnitudes of constrictor responses in lung slices vary over a very wide range of airway sizes; however, they did not include contraction/relaxation velocities in those comparisons. In the present study, in which a much smaller range of airway sizes was examined, neither the magnitudes nor the velocities of contraction were found to correlate in a statistically significant manner with airway size ( fig.…”