Cell membrane electropermeabilization by symmetrical bipolar rectangular pulses - Part I. Increased efficiency of permeabilization

The paper presents a comparative study of electropermeabilization of cells in suspension by unipolar and symmetrical bipolar rectangular electric puls es. While the parameters of electropermeabilization by unipolar pulses have been investigated extensively both in cell suspensions and in tissues, stu dies using bipolar pulses have been rare, partly due to the lack of commerc ially available bipolar pulse generators with pulse parameters suitable for electropermeabilization. We have developed a high-frequency amplifier and coupled it to a function generator to deliver high-voltage pulses of progra mmable shapes. With symmetrical bipolar pulses, the pulse amplitude require d for the permeabilization of 50% of the cells was found to be approximatel y 20% lower than with unipolar pulses, while no statistically significant d ifference was detected between the pulse amplitudes causing the death of 50 % of the cells. Bipolar pulses also led to more than 20% increase in the up take of lucifer yellow. We show that these results have a theoretical backg round, because bipolar pulses (i) counterbalance the asymmetry of the perme abilized areas at the poles of the cell which is introduced by the resting transmembrane voltage, and (ii) increase the odds of permeabilization of ce lls having a nonspherical shape or a nonhomogeneous membrane. If similar re sults are also obtained in tissues, bipolar pulse generators could in due c ourse gain a wide, or even a predominant use in cell membrane electropermea bilization. (C) 2001 Elsevier Science B.V. All rights reserved.