Electropermeabilization of cell plasma membrane is a threshold phenomenon. When a cell is exposed to electric field a spatially dependent transmembrane potential is induced (1 ). Above a certain threshold value of transmembrane potential permeability of plasma membrane drastically increases. Thus, in order to obtain plasma membrane permeabilization an above threshold transmembrane potential needs to be obtained. This is achieved by an above threshold electric field intensity. Electropermeabilization is therefore characterized by electric field intensity, but also by the duration and number of applied pulses, as well as their shape (2 ). Electric field intensity of the pulses of selected duration must reach a threshold, typical for a particular type of cell (3 ). This threshold is also different for the cells in tissue compared to the threshold for electropermeabilization of the membrane of isolated cells (4 ). Selected electric field intensity, appropriate for electroporation, should at the same time not exceed the value which will cause irreversible permeabilization or even death of the cell (5 ). This is particularly important for electro-gene transfection.
