Mechanically mimicking the membrane tension load induces lamellipodial actin buckling. (A) Schematic representation of the experiment. (B) Representative cell spreading inside a well. Actin in tirf (left), actin merged with DIC (middle), and zoom at the moment actin encounters the barrier. Arrows, two actin buckling events. (C) Time-lapse analysis of the actin buckling for stopped edge (a [red] and c [blue]) or unstopped edge (b [dark]). Graphs represent the intensity profiles of the selected a, b, and c regions of each frame (1–20) of the panel on top of the graphs. Green dashed lines are guides to determine the limit of each frame. (D) Representative frame and zooms showing actin fluorescence (tirf in red and epi in blue) of a cell attached to a 45-µm-diameter fibronectin circle (green). Arrow, buckled actin. (E) Representative frames showing actin fluorescence (tirf in red and epi in blue) of a cell attached to a 40-µm-diameter fibronectin circle (green) during iso-, hypo-, and hypertonic exchanges. Plot represents the variation in the overall cell area (square micrometers) of actin epi during each of the media exchanges. Dashed lines are guides to determine each medium exchange. Bars: (B, D, and E) 10 µm; (B [zoom 1] and C) 1 µm.