查看文章

We studied force-induced elongation of filopodia by coupling magnetic tweezers to the tip through the bacterial coat protein invasin, which couples the force generator to the actin bundles (through myosin X), thus impeding the growth of the actin plus end. Single force pulses (15–30 s) with amplitudes between 20 and 600 pN and staircase-like force scenarios (amplitudes, ∼50 pN; step widths, 30 s) were applied. In both cases, the responses consist of a fast viscoelastic deflection followed by a linear flow regime. The deflections are reversible after switching off the forces, suggesting a mechanical memory. The elongation velocity exhibits an exponential distribution (half-width <v_1/2>, ∼0.02 μm s⁻¹) and did not increase systematically with the force amplitudes. We estimate the bending modulus (0.4 × 10⁻²³ J m) and the number of actin filaments (∼10) by analyzing filopodium bending fluctuations. Sequestering of …