Figure 6. Membrane mechanical adaptation is explained by minimization of the strain and adhesion energies required to generate surface and volume containers.

(a) Phase diagram showing the predicted structures that require minimal energy to deform the membrane and detach it from the substrate in order to accommodate membrane surface area (upon stretch release) and liquid volume at the cell–substrate interface (upon an increase in osmolarity)18. Surface storage is achieved optimally with increasingly long tubules, whereas volume storage leads to the formation of spherical caps (VLDs). When both volume and surface storage are required, spherical caps ‘bud' and become more invaginated. (b) Left: time-course sequences of cell membrane regions showing the formation of either reservoirs or increasingly long tubules after releasing different stretch magnitudes. Right: Mean reservoir/tubule length (black dots, experimental data, red line, theoretical prediction) as a function of de-stretch magnitude (for increasing stretch, n=80/50/50 structures from 6/3/3 cells). (c) Left: images showing the formation of increasingly large VLDs after restoring iso-osmotic medium in cells previously exposed to different magnitudes of hypo-osmotic shocks for 3 min. Right: mean VLD diameter (black dots, experimental data, red line, theoretical prediction) as a function of hypo-osmotic shock magnitude (for increasing osmotic shock, 60/100/100/50 structures from 5/5/10/3 cells). Scale bars, 5 μm. Error bars are mean±s.e.m.