Fig. 4. Intracellular association with F-actin increases extracellular cadherin binding strength. (A,B) Differentiated myofibroblasts were grown on tipless AFM cantilevers in control conditions (A) or treated for 30 minutes with 1 µM cytochalasin D to depolymerize F-actin (B). Cells were immunostained for -SMA (green) and nuclei (blue) and images were taken with a confocal microscope. (C,D) AFM was used in imaging mode to probe the topography of monolayer cells before (C) and after cytochalasin D treatment (D); false-color intensity increases with cell height. (E) Differentiated myofibroblasts grown on tipless AFM cantilevers were put into contact for 2 seconds with myofibroblasts grown in monolayer using 3 nN loading force and an approach velocity of 0.1 µm/second (n>1500). All measured rupture forces are accumulated in histograms that were fitted with Gaussian curves and normalized to the total number of events. Contact was performed in the presence of cytochalasin D (solid red line) and compared with histograms obtained by putting into contact differentiated myofibroblasts in control conditions (dashed black line) (Fig. 1I) and by putting into contact recombinant OB-cadherins (solid black line) (Fig. 1C). Note that actin depolymerization reduces intrinsic binding of native myofibroblast cadherins to the level of recombinant OB-cadherin dimers. Scale bar: 50 µm.