Time domain-based impedance measurements were used to study the changes in electrical parameters of biological samples following the application of ultrashort high voltage (HV) pulses. Pulses with very short duration (300 ns) caused a significant drop in post pulse resistance of the plasma membrane only at high field strengths in excess of 20 kV/cm. The conductivity of the plasma membrane returned to almost pre-pulse values within less than 10 ms after the field was applied. Further steps of recovery, attributed to pore shrinking and resealing with an exponential decay of the conductivity, as is expected in electroporation, were not observed. An increase in medium conductance, as recorded minutes after the pulse, arises mainly from cell damage. Although pore formation is a possible effect of the high electric field, our results suggest further disturbance of the membrane-like micelle formation or even the creation of large defects, forced by mechanical tension within the cell membrane.
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