ABSTRACT
Giant lipid vesicles are cell-sized, topologically closed compartments consisting of soft, semipermeable membrane shells, which isolate femto- to picoliter quantities of aqueous core from the bulk. Although water permeates readily across the membrane boundary, passive permeation of solutes is strongly hindered generating osmotic gradients between the compartmentalized volume and the surrounding free bath. The osmotic relaxation process, which ensues, involves rapid movement of water across the membrane boundary inducing a dramatic deformations and structural rearrangements. Here, we assemble insights drawn from a collection of experimental and theoretical efforts, which cumulatively describe the variety of biophysical mechanisms that are activated when vesicular compartments are subject to osmotic perturbations. Although living cells respond to osmotic stresses by activating more complex protein machineries (e.g., mechanosensitive channels and biochemical pathways accumulating osmolytes), these efforts highlight membrane’s roles in sensing and regulating vesicular response to osmotic stresses. They may also shed light on how primitive protocells, devoid of sophisticated protein machineries, might have survived (and possibly benefited from) the pervasive osmotic challenges.
