Figure 1

Left panel: an example of the $F\text{−}z$ fit to the Hertz model of Eq. (1) for an NRK-193 cell. The parameters of the fit to Eq. (1) are $a=0\mathrm{pN}∕\mu \mathrm{m}$, $b=8\mathrm{pN}$, $k=396\mathrm{pN}∕\mu {\mathrm{m}}^{1.5}$, $z_0=-1.2\mu \mathrm{m}$. These parameters correspond to $E=94\mathrm{Pa}$. Right panel: the residuals of the fit are randomly scattered and well fit by a Gaussian (not shown) and the runs test has probability of 0.88.Reuse & Permissions

Figure 2

The height (a) and stiffness (b) of an astrocyte subjected to a challenge of $250\mathrm{mOsm}$ $5\min$ into the record (arrow). The cells swelled and showed a partial RVD but the cell softened after swelling. Each data point represents the parameters obtained from a fit such as that shown in Fig. 1.Reuse & Permissions

Figure 3

The response of astrocytes to a $250\mathrm{mOsm}$ osmotic challenge under various conditions. (a) Dark grey bars ($h_{2\min }$, left ordinate) are the peak swelling height at $2\min$ after solution change normalized by the resting cell height $h_r$. Note that cells swelled under all conditions. The ratio of the peak height $h_{2\min }$ to the steady state height $h_{ss}\sim 15\min$ from challenge, formed a simple measure of RVD which was mild even in control cells. All the cells shrank with time after the peak. (b) This scatter plot shows that none of the treatments caused swollen cells to become stiffer. The points are the mean value of $E$ at peak swelling and normalized by $E_0$, the stiffness at rest. Note that the cross-linking fixative, formaldehyde, did not stiffen the cell suggesting that it was naturally cross-linked before fixation.Reuse & Permissions

Figure 4

All cell types tested swelled with a hypoosmotic challenge (a) but none of them became significantly stiffer (b). (a) The mean peak height $h_{2\min }$ normalized by the resting height $h_r$. The scatter plot of (b) shows the Young’s modulus at peak swelling for different cells $E$ normalized by the modulus at rest $E_0$.Reuse & Permissions

Figure 5

A comparison of different methods used to stiffen HEK293 cells showing that intracellular hydrostatic pressure $<0.02\mathrm{Atm}$ applied through a patch pipette is by far the most effective means to stiffen the membrane. The numbers over the bars are the estimated indentation of the probe (nm) with an applied force of $20\mathrm{pN}$. These data were obtained with standard pyramidal point Veeco Microlever B $(k=0.02\mathrm{N}∕\mathrm{m})$ probes. ${\mathrm{Gd}}^{+3}$ was applied at $10\mu \mathrm{M}$ and formaldehyde at 10%. (b) Cartoon showing how inflation of the cell through the patch pipette can stiffen the membrane if it separates from the cytoskeleton.Reuse & Permissions