Electroporation threshold

Above some electroporation threshold, the transmembrane potential cannot be further increased, and can even decrease due to transport of ions across the membrane [91, 95]. The phenomenon of membrane electroporation can also be understood in terms of tension. If the total membrane tension exceeds the lysis tension c ys, the vesicle ruptures. This corresponds to building up a certain critical transmembrane potential, = Pc- According to Eqs. (7.3) and (7.4), this porahon potenhal Pc depends on the inihal membrane tension Co as previously reported [59, 89, 90, 96, 97]. The crihcal hansmembrane potenhal for cell membranes is about IV (e.g., [98, 99]). 

Ultrasound also exhibited a synergistic effect with electroporation [72], Ultrasound reduced the threshold voltage for electroporation as well as increased transdermal transport at a given electroporation voltage. The enhancement of transdermal transport induced by the combination of ultrasound and electroporation was higher than the sum of the enhancement induced by each enhancer alone. 

Cells in tissues are rarely spherical, but rather have all types of shapes, from ellipsoid to square to stellate. This affects deformation in response to the field and the threshold for electroporation may depend on the direction of the field versus the orientation of the cell. 

In tissues, the extracellular volume is small compared to the intracellular volume-completely the opposite of the situation when performing in vitro electroporation where the suspension medium volume by far exceeds the intracellular volume. This means that the threshold for electroporation is lowered [5]. It also means that the cell may tolerate permeabilization better, for example, since loss of ionic homeostasis may be less pronounced [6]. 

Gehl, J., Sorensen, T.H., Nielsen, K., Raskmark, P., Nielsen, S.L., Skovsgaard, T., et al. (1999) In vivo electroporation of skeletal muscle threshold, efficacy and relation to electric field distribution. Biochimica et Biophysica Acta, 1428, 233-240. 

When the induced membrane potential exceeds a certain threshold value, the dielectric breakdown occurs. The dielectric breakdown generates pores in the phospholipid cell membrane. These pores are generated reversibly, and they are sealed spontaneously with the self-assembly of phospholipid molecules. The amount of membrane potential required to initiate electroporation is known to be approximately 1 V. 

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