Selected contribution: Plasticity of airway smooth muscle stiffness and extensibility: role of length-adaptive mechanisms

Airway smooth muscle exhibits the property of length adaptation, which enab les it to optimize its contractility to the mechanical conditions under whi ch it is activated. Length adaptation has been proposed to result from a dy namic modulation of contractile and cytoskeletal filament organization, in which the cell structure adapts to changes in cell shape at different muscl e lengths. Changes in filament organization would be predicted to alter mus cle stiffness and extensibility. We analyzed the effects of tracheal muscle length at the time of contractile activation on the stiffness and extensib ility of the muscle during subsequent stretch over a constant range of musc le lengths. Muscle strips were significantly stiffer and less extensible af ter contractile activation at a short length than after activation at a lon g length, consistent with the prediction of a shorter, thicker array of the cytoskeletal filaments at a short muscle length. Stretch beyond the length of contractile activation resulted in a persistent reduction in stiffness, suggesting a stretch-induced structural rearrangement. Our results support a model in which the filament organization of airway smooth muscle cells i s plastic and can be acutely remodeled to adapt to the changes in the exter nal physical environment.