Cell membrane thermal gradients induced by electromagnetic fields

While electromagnetic fields induce structural changes in cell membranes, particularly electroporation, much remains to be understood about membrane level temperature gradients. For instance, microwaves induce cell membrane temperature gradients (del T) and bioeffects with little bulk temperature change. Recent calculations suggest that nanosecond pulsed electric fields (nsPEFs) may also induce such gradients that may additionally impact the electroporation threshold. Here, we analytically and numerically calculate the induced del T as a function of pulse duration and pulse repetition rate. We relate del T to the thermally induced cell membrane electric field (E-m) by assuming the membrane behaves as a thermoelectric such that E-m similar to del T. Focusing initially on applying nsPEFs to a uniform membrane, we show that reducing pulse duration and increasing pulse repetition rate (or using higher frequency for alternating current (AC) fields) maximizes the magnitude and duration of del T and, concomitantly, E-m. The maximum del T initially occurs at the interface between the cell membrane and extracellular fluid before becoming uniform across the membrane, potentially enabling initial molecular penetration and subsequent transport across the membrane. These results, which are equally applicable to AC fields, motivate further studies to elucidate thermoelectric behavior in a model membrane system and the coupling of the E-m induced by del T with that created directly by the applied field. (C) 2013 AIP Publishing LLC.