Changes in biophysical and biochemical properties of single bronchial smooth muscle cells from asthmatic subjects

Abstract

Whether contractility of bronchial smooth muscle cells (BSMC) from asthmatic subjects is significantly altered has never been validated. We tested the hypothesis that such BSMC show increased contractility. Cells were isolated from endobronchial biopsies. BSMC shortening was measured under an inverted microscope. Statistically significant increases in maximum shortening capacity (Delta L max) and velocity (Vo) were found in asthmatic BSMC compared with normal cells. Mean Delta L max in asthmatic BSMC was 39.05 +/- 1.99% (SE) of resting cell length compared with 28.6 +/- 1.1% in normal cells; mean Vo was 7.2 +/- 0.8% of resting cell length/s in asthmatic cells and 5.23 +/- 0.46% in normal cells. To investigate the mechanism of the increased contractility, we measured mRNA abundance of smooth muscle types of myosin light chain kinase (smMLCK) and myosin heavy chain. RT-PCR data revealed that smMLCK mRNA was higher in asthmatic BSMC (0.106 +/- 0.021 arbitrary densitometric units, n = 7) than in control cells (0.04 +/- 0.008, n = 11; P < 0.05). Messages for myosin heavy chain isoforms showed no difference. Increased kinase message content is an index of the mechanism for the increased velocity and capacity of shortening we report.

Asthma: where is it going?

“…ASM velocity of shortening plays a significant role in determining the maximal extent of smooth muscle shortening for a given load (22), supporting its relevance to airway hyperresponsiveness (8). These findings suggest that the cell itself seems to be mechanically different, supporting the argument that ASM cells are the seat of primary changes in the mechanical properties of the asthmatic airways (14).…”

“…Functional changes have been reported in the ASM behavior of asthmatic patients, suggesting that the intrinsic contractile properties of ASM are altered in asthma (8,13,14). Increased response to contractile agonists (15,16) and reduced response to dilator agonists have been well documented (11,17).…”

“…On the other hand, the alternative hypotheses were consistent with remodeling events induced by an inflammatory microenvironment, e.g., changes of muscle mass, changes of the static load against which the muscle shortens, and changes of the dynamic load of myosin binding. In humans, however, bronchospasm has been reported in the absence of acute inflammation in exercise-induced asthma, with no significant increase in bronchoalveolar lavage levels of inflammatory mediators and/or cells (14). Indeed, the extent and functional implications of the various elements present during remodeling are uncertain (8).…”

“…In addition, increased velocity of muscle shortening has been demonstrated in animal models of airway hyperresponsiveness (21,23), and in human ASM from asthmatic patients, in which these functional differences were associated with an increased message for myosin light chain kinase (14). ASM velocity of shortening plays a significant role in determining the maximal extent of smooth muscle shortening for a given load (22), supporting its relevance to airway hyperresponsiveness (8).…”

Force Fluctuation induced Relengthening of Acetylcholine-contracted Airway Smooth Muscle

“…Work from Newman Stephens laboratory has demonstrated increased expression of myosin light chain kinase (MLCK) in airway smooth muscle from individuals with asthma and a ragweed-sensitized dog model of airway hyperresponsiveness (16,17). Airway smooth muscle from these individuals with asthma and from sensitized dogs concomitantly demonstrated increased shortening velocity and capacity (17,18).…”