Comment: “Microwave irradiation influences on the state of human cell nuclei” [Y.G. Shckorbatov et al., 19:414—419 (1998)]

Schkorbatov et al. [1998] report that millimeter wave radiation changes the electrokinetic properties of nuclei in `̀ intact'' cells. Simple biophysical considerations would seem to rule out this interpretation. The investigators measured the electrokinetic properties of buccal epithelium cells scraped from the cheeks of human subjects, using an applied electric ®eld of 15 V/cm. They judged a nucleus as being negatively charged if it is `̀ displaced to the anode'' as observed by visual examination under a microscope. But if the cell is really intact, its inside will be shielded from the external ®eld by a factor of many thousands. This rules out the possibility of observing electrokinetic effects of the nuclei of intact cells. An external low-frequency ®eld simply does not reach the nucleus, at least at levels that will cause visible electrophoretic responses. For example, for a spherical cell of radius R in an initially unperturbed electrical ®eld Eo, the ®eld Ei inside the cell is approximately 1.5 EoRriGm where ri is the resistivity of the cytoplasm and Gm is the membrane conductance [Foster and Schwan, 1995]. For typical cell parameters (Rˆ 10mm, Gmˆ 1 S/m) this corresponds to a reduction in ®eld by a factor of 100,000, to levels far below those needed (tens of V/cm) to cause visible electrophoretic movements of the nuclei. It is hard to imagine any reasonable variation of this calculation, either in the shape of the cell or in its membrane conductance, that would result in induced ®elds at the nucleus that would be suf®cient to cause visible dielectrophoretic movement of the nucleus. (In long cylindrical cells, such as muscle ®bers or nerve axons, the situation might be different). I conclude that either the cells were not electrically intact, or the investigators did not observe electrophoretic forces on the nuclei. Few experimental details are provided in this or in other papers from the group in English-language journals that I had access to, and it is dif®cult to judge the reliability of the qualitative observations on which the study is based. If the observations were correct, the simplest explanation is that the cells whose nuclei `̀ displaced to the anode'' had damaged plasma membranes, and the investigators were reporting differences in the fraction of membrane-damaged cells, a simple artifact. Alternatively, the cells might have been intact, but the investigators (mis)interpreted electrophoretic forces exerted elsewhere on the cells as being due to the action of the ®elds directly on their nuclei. `̀ Forces applied to a cell are distributed over many components, including the extracellular matrix, the bilayer, and the cytoskeleton'' Akinlaja and Sachs [1998] recently observed, and `̀ the latter distributes forces within the cell cortex and as deep as the nucleus''. The proper interpretation of the study, if indeed the observations are correct, remains unclear.