Tube extrusion from permeabilized giant vesicles

This letter reports the permeabilization effects of chemical additives on mechanical properties of Giant Unilamellar Vesicles (GUVs). We use a surfactant, Tween 20, inducing transient pores and a protein, Streptolysin O, inducing permanent pores in the membrane. Lipid tubes are extracted from GUVs anchored onto the tip of a micro-needle and submitted to hydrodynamic flows. On bare vesicles, tube extrusion is governed by the entropic elasticity of the membrane. The vesicle tension increases until it balances the flow velocity U and the tube reaches a stationary length. In permeabilized vesicles, the membrane tension is maintained at a constant value sigma(p) by the permeation of inner solution through nanometric pores. This allows extrusion of "infinite" tubes at constant velocity that never reach a stationary length. Tween-20 preliminary results suggest that sigma(p) strongly depends on surfactant concentration. For Streptolysin O, we have measured sigma(p) vs. U and found two regimes: a "high-porosity" regime for U > U-p0 and a "low-porosity" regime for U < U-p0, where U-p0 is related to the number of pores on the vesicle surface.