Influence of myosin II activity on stiffness of fibroblast cells.

Myosin II is responsible for establishing cytoskeleton tension within eukaryotic cells. We used an atomic force microscope to quantify the cells mechanical properties as a function of myosin activity. In two fibroblast cell lines, the elastic modulus of the cytoskeleton decrease by a factor of 3-5 regardless of location and cell type after inhibition of myosin II light chain kinase. We used two different inhibitors (BDM and ML-7) and observed the effects on two different fibroblast cell lines (3T3 and NRK). The cells stopped migration, retracted their lamellipodia, and softened by a factor of 3 in peripheral and in nuclear regions. The observed effect was concentration dependent. Application of the inhibitor at very low concentration had no effect on morphology or mechanical properties, whereas application of high concentration was usually lethal. At an intermediate range of concentrations, retraction of lamellipodia and softening of cells occurred, from which the cells recovered within an hour.