Linear Correlation between Active and Resistive Stresses Provides Information on Force Generation and Stress Transmission in Adherent Cells.

Animal cells are active, contractile objects. While bioassays address the molecular characterization of cell contractility, the mechanical characterization of the active forces in cells remains challenging. Here by confronting theoretical analysis and experiments, we calculated both the resistive and the active components of the intracellular stresses that build up following cell adhesion. We obtained a linear relationship between the divergence of the passive stress and the traction forces, which we show is the consequence of the cell adhering and applying forces on the surface only through very localized adhesion points (whose size is inferior to our best resolution, of 400 nm). This entails that there are no measurable forces outside of these active point sources, and also that the passive stresses and active stresses inside cells are proportional.