THE CONTRACTILE APPARATUS OF AIRWAY SMOOTH-MUSCLE - BIOPHYSICS AND BIOCHEMISTRY

Qualitatively the mechanical, structural, and biochemical properties o f airway smooth muscles resemble those of all other smooth muscle. How ever, one important distinguishing feature of airway smooth muscle is that the major portion of isotonic shortening is completed within the first 3 s in a muscle whose contraction is 10 s. This indicates the im portance of focusing on the changes that occur in these 3 s and also t he limiting role of the maximum velocity of shortening in determining shortening data. There is evidence that the maximum capacity and veloc ity of shortening in human bronchial smooth muscle from patients with asthma are significantly greater than those obtained from healthy sibl ings. In the demonstration in which cells in culture are arrested by w ithdrawing all fetal calf serum, the cells alter their phenotype to ce lls that are very long (more than 200 mu m) and shorten twice as much as cells freshly isolated when the tissue is new. Speculatively, if su ch cells developed in vivo they could account for the increased contra ctility of asthmatic airway smooth muscle. These cultured cells could also be excellent models for study of airway smooth muscle contractili ty.