Giant vesicles - a handy tool for mimicking the cell membrane

Vesicles are closed lipid bilayer compartments with an internal water core. Giant vesicles, in contrast to conventional ones (~ 100nm), have the advantage that they can be observed using optical microscopy. These giants, being only a few tens of microns in size, are quite a handy tool for studying the mechanical properties of lipid bilayers, because the physical characteristics of the membrane can be obtained from working with individual vesicles. A large variety of techniques have been developed for assessing the elastic properties (bending modulus, stretching elasticity, spontaneous curvature) and the hydrodynamic features (shear surface viscosity) of the lipid bilayer. A few of them will be presented in this talk. Giant vesicles have been also used for direct observation and measuring the properties of lipid membranes when undergoing phase transitions. A dramatic increase of the membrane surface viscosity as well as the bending stiffness of the membrane was detected for membranes crossing the fluid-to-gel phase transition.

The interaction of electric fields with lipid membranes and cells has been extensively studied in the last decades. The phenomena of electroporation and electrofusion are of particular interest because of their widespread use in cell biology and biotechnology. However, direct optical microscopy observation of effects caused by electric DC pulses on giant vesicles is difficult because of the short duration of the pulse. Recently this difficulty has been overcome in our lab. Using a digital camera with high temporal resolution, we were able to access the dynamics of electro-deformation, -poration and -fusion of vesicles on a sub-millisecond time scale. Results from these observations will be presented.