As its name indicates, the technique of cell electroporation consists in inducing pore formation in living cells through the action of an electric field. These pores are repaired quickly after the end of the electric discharge and, while open, make cells permeable to a whole host of compounds, including DNA.
Poration occurs only after the membrane breakdown voltage has been reached. The electric field strength necessary to reach this voltage can be calculated using the simplified Laplace equation:
where V (in volts) is the breakdown voltage (equal to approximately 1V for living cells), r (in cm) is the radius of the cell, and E is the electric field strength in volts/cm. E thus depends on both the set voltage and the distance between the electrodes. Most plant protoplasts experience membrane breakdown around 250 V/cm.
Once the breakdown voltage has been reached or exceeded, the amount of compound (such as DNA or RNA) that will be internalized depends on the electrical energy (in joules, J) dissipated in the system per unit volume (EDV). If the pulse is delivered by a capacitance, the energy W is
where C is the value of the capacitance in farads and V is die set voltage in volts. In die case of a square wave pulse, thenergy is