Displacement field of the cytoskeleton in response to a local load

Mechanical stresses acting on the apical cell surface are transmitted to the anchoring sites of the cell via cytoskeletal polymers, but details of the stress-, strain- or deformation field within the cell are largely unknown. Here we have measured the deformation field within cultured smooth muscle cells in response to small stresses. Stresses were applied to integrin receptors on the cell surface via magnetic microbeads (4.5 μm diameter). The beads were torqued in a sinusoidally varying magnetic twisting field (specific torque amplitude of 90 Pa, frequency 0.3 Hz). Cells were transfected to express either fluorescent mitochondria, microfilaments, or microtubules. Ten images were taken during each of ten or more twisting cycles, from which we computed the deformation field within the cell. Our results confirm that mechanical stresses in cells can be transmitted via focal adhesions on the apical cell surface to the internal cytoskeleton. Importantly, cytoskeletal deformations in most cells decayed to below the resolution limit within a short distance (∼5μm) from the locus of stress application.