Figure 2.

To calculate the effective tension from the fluctuations of the bleb edge, we explored two different methods that both rely on a separation of timescales. (A) The power spectrum of the edge movement for the data shown in panel B) is calculated, and the power law of −1 is detected in the high-frequency part. The prefactor for this region of the PSD depends on the effective tension. (B) The edge movement x(t) (blue) is averaged to determine the bleb extension x_bleb (red). The membrane fluctuations are recovered as the difference between edge movement and bleb extension x_fluc = x − x_bleb (black). (Inset) Using the determined fluctuations, we construct a position histogram and fit a Gaussian distribution to it. The variance of the Gaussian is related to the tension of a free membrane. (C) To determine the smoothing window size, the SD of x_fluct(τ) is determined as a function of τ. (Black) Directly determined SD. The long time slope is determined and subtracted from the original function to obtain the corrected SD (red). The idea of the correction is to remove the effect of the continuous growth on the SD. The maximum of the resulting function is used as an estimate for the window size. (Blue dotted line) Timescale for the smoothing in this example.