ABSTRACT
A long-standing guiding model for the analysis of the e ects of pulsed and AC electric elds on biological cells is the dielectric shell, in which the cell is a membrane-bound ellipsoidal volume of a conductive µuid suspended in an external conductive medium (Plonsey and Altman, 1988). To represent the properties of real cell suspensions, the membranes are assigned a low permittivity and a low conductivity, and the media have relatively much higher permittivities and conductivities. Ions and other charged species migrate in the conductive intracellular and extracellular media in the presence of an electric eld, accumulating at the essentially impermeable membrane-medium interfaces, where the resulting charge separation across the membrane produces a transmembrane potential. Because the membrane is so thin (about 5nm), this charge accumulation e ectively magni es the externally applied eld a thousand-fold or more in the membrane interior, with the maximum value occurring where the applied eld is normal to the membrane surface. When the transmembrane potential exceeds a critical value (400mV-1V), the membrane becomes electrically conductive and permeable to ions and small molecules (Kinosita and Tsong, 1977; Zimmermann, 1982; Teissie and Rols, 1993). e inµux of µuorescent dyes like propidium iodide (PI), a salt of the divalent propidium ion (the solubilized cation is the actual µuorochrome), which do not pass through intact membranes, is a common diagnostic for this electric eld-driven restructuring of the membrane, which results in permeabilization.
