Mechanical interactions among cytoskeletal filaments.

Mechanical properties of the cells are important in controlling cell shape, cell migration, and other functions. To understand how cytoskeletal (CSK) filaments interact with one another mechanically, mechanical properties of adherent endothelial cells were analyzed after treatment with CSK-disrupting drugs. CSK stiffness (the ratio of applied stress to strain, a measure of cell resistance to shape deformation), viscosity (an index of intracellular structural damping), and permanent deformation (a measure of "plasticity") were measured with magnetic twisting cytometry, by which rotational stress was applied directly to integrin receptors with ferromagnetic beads coated with RGD-containing peptide. Treatment with cytochalasin D, which disrupts actin microfilaments inhibited stiffness by 50% and decreased permanent deformation from 70% to 50% but had almost no effect on viscosity. In contrast, nocodazole, a microtubule disrupter, had very little effect on inhibition of CSK stiffness, decreased viscosity by 25%, and had no effects on permanent deformation. Acrylamide, an intermediate filament disrupter, had little effect on inhibition of CSK stiffness, little effect on viscosity, and no effect on permanent deformation. Taxol, a drug that facilitates microtubule polymerization, increased stiffness by 10%, increased viscosity by 10%, and decreased permanent deformation from 70% to 50%. Combinations of cytochalasin D and nocodazole, cytochalasin D and acrylamide, or all three drugs resulted in a synergistic effect on inhibition of CSK stiffness and viscosity but not in permanent deformation. Inhibition of oxidative metabolism with potassium cyanide had no effects on stress-induced stiffening response. Inhibition of tyrosine phosphatase with phenylarsine oxide had no effect on stress-induced stiffening response. We conclude that higher order mechanical interactions of CSK filaments are important in determining the mechanical properties of the cell.