Optical measurement of the viscoelastic and biochemical responses of living cells to mechanical perturbation.

We have developed an optical method for real-time monitoring of cellular motion in a natural environment with nanometer resolution. From the motion driven by small optical forces, we measured dynamic viscoelastic responses of living cells in the linear reversible region. Cytoplasmic gel-to-sol transition that was due to the disruption of the actin-filament framework was detected, and a linear release of Ca(2+) from intracellular storage that was related to submicrometer cell deformation was observed. The method was shown to be a powerful tool for studying the natural response of cells to mechanical perturbation.