Selected Contribution: Mechanical strain increases force production and calcium sensitivity in cultured airway smooth muscle cells

Cultured airway smooth muscle cells subjected to cyclic deformational strai n have increased cell content of myosin light chain kinase (MLCK) and myosi n and increased formation of actin filaments. To determine how these change s may increase cell contractility, we measured isometric force production w ith changes in cytosolic calcium in individual permeabilized cells. The pCa for 50% maximal force production was 6.6 +/- 0.4 in the strain cells compa red with 5.9 +/- 0.3 in control cells, signifying increased calcium sensiti vity in strain cells. Maximal force production was also greater in strain c ells (8.6 +/- 2.9 vs. 5.7 +/- 3.1 muN). The increased maximal force product ion in strain cells persisted after irreversible thiophosphorylation of myo sin Light chain, signifying that increased force could not be explained by differences in myosin light chain phosphorylation. Cells strained for brief periods sufficient to increase cytoskeletal organization but insufficient to increase contractile protein content also produced more force, suggestin g that strain-induced cytoskeletal reorganization also increases force prod uction.