FIGURE 3.

Force maps on endothelial cells in real-time. (A–C) Specific interaction probed with a Si₃N₄ tip functionalized with anti-Flk-1. (A) Force map. (B) Force curves taken at various points on the cell from the map shown in A. The curves are offset with respect to zero force. (C) Probability histogram of the unbinding forces of the force curves from the force map in A. The histogram is fitted with a Gaussian and the corresponding maxima and σ is indicated in the figure. The dominant unbinding force ∼60–70 pN suggests breakage of single receptor-antibody bonds. (D–F) Competitive inhibition probed with the anti-Flk-1 functionalized Si₃N₄ tip, 10 min after adding antibody in the recording medium. The panels correspond to A–C. The characteristic unbinding force is suppressed and the measured forces are shifted toward higher values. (G–I) Corresponds to A–C, but at 45 min after adding antibody in the recording medium. The micrometer-sized brighter spots in G are identified as receptor clusters. A few of the clusters are marked by numbers 1–4.