Fig. 4: Rounded HeLa cells maintain no universal pressure or tension.
From: Rheology of rounded mammalian cells over continuous high-frequencies
a Average power-law behavior of unperturbed HeLa cells (black) in the absence and in the presence of 500 nM LatA (purple) or 50 µM CK666 (red) (n = 10 biologically different cells for each condition), corresponding mean values and standard deviations are given in Supplementary Table 2. The storage modulus \({E}_{{\rm{cort}}}^{{\prime} }\) is plotted as a dotted line and the loss modulus \({E}_{{\rm{cort}}}^{{\prime} {\prime} }\) as a through line for each condition. b Applying Laplace’s law to a population of rounded cells gives two simple scenarios: i) bigger cells are stiffer, if a universal pressure exists, or ii) bigger cells are softer, if a universal tension exists. c, d Relative variations of storage and loss moduli of unperturbed (purple-gray), LatA perturbed (purple-red), and CK666 perturbed (purple-blue) HeLa cells plotted against the cell radius R and frequency \(f\). Negative and positive relative moduli describe the cell to become softer and stiffer, respectively. Frequency-dependent variations of both moduli are best visualized by the yellow reference plane. The hypothesis of no correlation with R could not be rejected, as the t-test resulted in p-values of 0.95 and 0.92 (Methods). Red and pink planes indicate hypothetical dependencies proportional to 1/R (constant pressure) and 1/R2 (constant tension), respectively. An independency of cell size is found for every individual parameter of the power-law A, B, α, and \(\beta\) (Supplementary Fig. 14). e STED super resolution nanoscopy of paraformaldehyde-fixed HeLa cells with SiR-actin stained F-actin. Scale bars, 5 µm and 500 nm (inset). f For each of the 10 HeLa cells imaged by STED nanoscopy, we fitted 10 line profiles of the SiR-actin signal, to extract the cortical thickness hcort (194 ± 27 nm, mean ± S.D.). The center bar indicates the mean, the whiskers show the standard deviation. The diameter and cortex thickness measured for each cell by STED microscopy is shown in Supplementary Fig. 15.
