Mechanical strain increases velocity and extent of shortening in cultured airway smooth muscle cells

Abnormal mechanical stress on lung tissue is associated with increased mass and contractility of airway smooth muscle (ASM). We have reported that cul tured ASM cells subjected to cyclic strain exhibit increased myosin light c hain kinase (MLCK) and stress filaments, increased MLCK may increase contra ctile velocity, whereas increased stress filaments could impede cell shorte ning by increasing the cell's internal load. To study strain-induced change s in cell contractility, the time course of shortening of individual cells exposed to 90 mM KCl was recorded. Length vs. time plots revealed significa ntly greater maximal velocity of shortening in strain cells than control (n o strain). This correlated with an increase in MLCK and myosin light chain phosphorylation measured in strain cells in separate experiments. The exten t of cell shortening tended to be greater in the strain cells so that incre ased impedance to shortening was not detected. Mechanical stress may theref ore increase the contractility of ASM by increasing the content of MLCK.