Electromechanical deformation of mammalian cells in suspension depends on their cortical actin thicknesses.

The mechanical properties of mammalian cells are largely determined by their cytoskeletons (CSKs), which comprise several distinct but interacting cytoplasmic molecular networks. To examine the influence of the CSK on cell mechanical properties, we deformed several mammalian cell-types (L929, CHO, HEK293, and U937) in suspension using time-varying non-uniform electric fields. Confocal fluorescent microscopy was also used to visualize and semi-quantitatively analyze CSK dimensions. We found mechanical properties of individually deformed cells to depend on cortical actin (CA) thickness. U937 and HEK293 cells with thin CA were more easily deformed than CHO and L929 cells, which bore thicker CA. In additional experiments, we treated U937 cells with latrunculin-A (Lat-A) and acrylamide (ACR), drugs that disrupt microfilaments (MF) and intermediate-filaments (IF), respectively, in order to assess their effects on the CSK and on the cell mechanical properties. We fit strain data using either a power-law or a viscoelasticity model of compliance. Our results demonstrated that maximal strain values observed under identical loading conditions were determined by the structural integrity and thickness of CA in suspended cells. Young's modulus values of individually deformed cells that were estimated using a power-law model showed a linear dependence on cortical actin thickness.