Theoretical evaluation of the distributed power dissipation in biological cells exposed to electric fields

The paper deals with the power dissipation caused by exposure of biological cells to electric fields of various frequencies. With DC and sub-MHz AC fr equencies, power dissipation in the cell membrane is of the same order of m agnitude as in the external medium. At MHz and GHz frequencies, dielectric relaxation leads to dielectric power dissipation gradually increasing with frequency, acid total power dissipation within the membrane rises significa ntly. Since such local increase can lead to considerable biochemical and bi ophysical changes within the membrane, especially at higher frequencies, th e bulk treatment does not provide a complete picture of effects of an expos ure. In this paper, we theoretically analyze the distribution of power diss ipation as a function of field frequency. We first discuss conductive power dissipation generated by DC exposures. Then, we focus on AC fields; starti ng with the established first-order model, which includes only conductive p ower dissipation and is valid at sub-MHz frequencies, we enhance it in two steps, We first introduce the capacitive properties of the cytoplasm and th e external medium to obtain a second-order model, which still includes only conductive power dissipation. Then we enhance this model further by accoun ting for dielectric relaxation effects, thereby introducing dielectric powe r dissipation. The calculations show that due to the latter component, in t he MHz range the power dissipation within the membrane significantly exceed s the value in the external medium, while in the lower GHz range this effec t is even more pronounced. This implies that even in exposures that do not cause a significant temperature rise at the macroscopic, whole-system level , the locally increased power dissipation in cell membranes could lead to v arious effects at the microscopic, single-cell level. (C) 2000 Wiley-Liss, Inc.