A theory of osmotic lysis of lipid vesicles

Osmotic lysis of vesicles is shown to begin when the membrane expansion due to osmotic pressure exceeds its critical value, Δ~S, at which a membrane ruptures to form a pore. The dependence of Δ~S on the vesicle radius and respective osmotic pressures are obtained. It is found that osmotic pressure necessary for small (100 Å) vesicles to rupture should exceed 30 atm, for large (10 000 Å) vesicles it being as small as 10^-3 atm. In the case of large (≥ 1000 Å) vesicles the value of relative expansion of the membrane at which its rupture occurs in a reasonable time only depends slightly on the vesicle radius. For instance, for 10 000 Å vesicles it amounts to 3%. The tension of membrane rupture is about 8 dyn/cm for large vesicles. Membrane tension, although it decreases considerably as a result of rupture and pore formation, does not vanish completely. It supports the residual intravesicular pressure causing the efflux of vesicle (cell) contents. Simultaneously, osmotic influx of water through the membrane occurs that results in either complete rupture of the membrane with the efflux of the whole of the contents, or its gradual washout in either of two, quasi-steady or pulse-wise regimes. In the first case a pore is steadily open, whereas in the second case it alternately opens and closes, ejecting about 5% of internal solution each time. Lysis kinetics is analyzed. Pulse-wise regime of lysis is shown to be the most likely one.