Thermal action of 2.45 GHz microwaves on the cytoplasm of Chinese hamster cells

Abstract

In order to demonstrate possible specific effects of microwaves at the cellular level V-79 Chinese hamster cells were exposed to 2.45-GHz radiation at power levels of 20-200 mW/cm2 and at specific absorption rates of 10-100 mW/g. Intracellular cytoplasmic changes were observed by fluorescence polarization using a method based on the intracellular enzymatic hydrolysis of nonfluorescent fluorescein diacetate (FDA). At levels of absorbed energy below 90 J/g, modifications of microviscosity and mitochondrial state were absent, but a slight stimulation of enzymatic hydrolysis of FDA was observed which may be explained by microwave-induced alterations of cellular membranes possibly due to differences in heating pattern of microwaves compared to water-bath heating. At levels of absorbed energy above 90 J/g, the decrease of enzymatic hydrolysis of FDA, increase in degree of polarization, and increase of permeation of the fluorescent marker correlated well with the decrease in cell viability as measured by the exclusion of trypan blue. At equal absorbed energy, microwaves were found to exert effects comparable to classical heating except that permeation was slightly more affected by microwave than by classical heating. This suggests that membrane alteration produced by microwaves might differ from those induced by classical heating or that microwaves may have heated the membrane to higher temperatures than did classical heating.

Thermal Effects of 2·45 GHz Microwaves on Survival and Viability of Chinese Hamster V-79 Cells

“…These results are also valid when expressed as a function of absorbed energy and when taking into account a correction factor for energy losses according to Allis et al (1977) and Dardalhon et al (1984) . This is especially important since in contrast to waterbath-heated samples microwave-heated samples are known to diffuse part of their absorbed energy .…”

“…This suggests that the cellular damage induced by the two types of hyperthermia is quite comparable, although the mechanism of microwave-induced heating differs basically from that induced by conventional heating in that the latter corresponds to a thermal activation of mechanical vibrations (Berteaud 1982) . Recent measurements of changes in microviscosity of the cytoplasm, enzymatic hydrolysis and cell permeation induced by hyperthermia in Chinese hamster V-79 cells (Dardalhon et al 1984) have suggested that modifications of the membrane produced by microwaves rray differ from those produced by classical heating or that microwaves may have heated the membrane to a higher temperature than did classical heating . Such effects may also be related to the effects on survival observed in the present study for 150 and 175 mW/cm 2 .…”