Modification of membrane fluidity in melanin‐containing cells by low‐level microwave radiation

The treatment of a B16 melanoma cell line with 2.45‐GHz pulsed microwaves (10 mW/cm², 10‐μs pulses at 100 pps, 1‐h exposure; SAR, 0.2 W/kg) resulted in changes of membrane ordering as measured by EPR (electron paramagnetic resonance) reporter techniques. The changes reflected a shift from a more fluid‐like phase to a more solid (ordered) state of the cell membrane. Exposure of artificially prepared liposomes that were reconstituted with melanin produced similar results. In contrast, neither B16 melanoma cells treated with 5‐Bromo‐2‐Deoxyuridine (3 μg/day × 7 days) to render them amelanotic, nor liposomes prepared without melanin, exhibited the microwave‐facilitated increase of ordering. Inhibition of the ordering was achieved by the use of superoxide dismutase (SOD), which strongly implicates oxygen radicals as a cause of the membrane changes. The data indicate that a significant, specific alteration of cell‐membrane ordering followed microwave exposure. This alteration was unique to melanotic membranes and was due, at least in part, to the generation of oxygen radicals. © 1992 Wiley‐Liss, Inc.