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A transient increase of membrane permeability and conductivity is observed when a cell membrane or an artificial lipid membrane is exposed to a transmembrane potential difference in the order of 1 Volt. The basic mechanism of this phenomenon, which is the same in cells as well as in BLM, involves the following steps: formation of hydrophobic pores, increase in radius and inversion of the pores to hydrophilic ones by molecular rearrangement of pore edge. The electric field enhances pore widening mainly by forces rectangular to the field lines.
The hydrophilic pores permit small molecules to cross the membrane. However, ions have to overcome a considerable energy barrier so that pore conductivity shows a strong and nonlinear dependence on voltage.
There exists neither a threshold voltage for pore formation nor any qualitative change of the electric response of the membrane during reversible electrical breakdown.
