Quantitative kinematics of plasma membrane protrusions in thrombin-stimulated iMKs. (A-B) Representative time-lapse confocal microscopy imaging of the extension-retraction cycle for an individual filopodium (A) and a bleb (B) on a thrombin-stimulated iMK within a plasma clot (supplemental Videos 4 and 5). Scale bars, 1 μm. White arrowheads show snapshots of the filopodium and bleb at different time points of their extension and retraction phases. (C-D) Averaged kinematic curves for filopodia (C) and blebs (D) measured as an averaged distance of the protrusion tip from the iMK surface; each curve reveals the extension and retraction phases (mean ± 95% CI; 100 filopodia and 100 blebs analyzed in 21 cells). Significance tested using the Kolmogorov-Smirnov test. In panel C, protrusion kinematics curves for the smaller (<700 nm) and larger (>700 nm) blebs are shown in blue and red, respectively. Solid lines are log-normal fits $(A1/t)exp[−0.5(ln(t/A2)ln(A3))2]$⁠, (C, black curve) A₁ = 71.24, A₂ = 105.60, A₃ = 3.20; (D, red curve): A₁ = 95.57, A₂ = 94.27, A₃ = 2.30; (D, blue curve) A₁ = 29.26, A₂ = 70.85, A₃ = 2.84. Dashed lines indicate temporal borders between the extension and retraction phases (see supplemental Table 1). Statistical significance was tested by the Kruskal-Wallis test. (E) Extension and retraction rates for individual filopodia and smaller and larger blebs determined as the averaged slopes of the kinematic curves shown in panels C-D (median and IQR). The Mann-Whitney U test. IQR, interquartile range.