Percent detachment of VE-Cadherin coated beads on control (A), cytochalasin D treated (B), Ena/VASP inactivated (Mito, C), or VASP overexpressing (D) HUVEC in response to low (0.7 nN), high (2.1 nN), and ramped (from 0.7 nN to 2.1 nN over 50s of applied force). A decrease in the number of beads detaching between high and ramped force conditions would be consistent with force strengthening (A). Disruption of the actin cytoskeleton or inactivation of Ena/VASP blocks force strengthening (B, C). While overexpression of VASP appears to slightly increase basal binding strength, it also leads to weaker adhesions in the presence of ramped force (D). For a given cell type, significant difference to low force, determined with Fisher's one-tailed exact test (p<0.005), is indicated with (*). Significant difference (p<0.05) from the same force profile for control HUVECs is indicated with (+).