Changes in membrane fluidity of retinal photoreceptor cells induced by low level microwave irradiation

Extensive electromagnetic exposure in everyday life requires a better understanding of the effects of electromagnetic radiation on living organisms as more as cellular responses to very low level stimuli were observed. In this paper we study the effects of low power microwaves on retinal photoreceptor cell membrane by monitoring the changes induced in the membrane fluidity; the cell membrane fluidity is important for the proper functioning of the enzyme systems involved in the visual signal transduction pathway. The retinae from dark adapted frogs (Rana ridibunda) were dissected in dim red light and the rod cells suspension was prepared by gently shaking 12 retinae in 1 ml of Ringer solution. The membrane fluidity of irradiated and control photoreceptor cells was monitored by fluorescence anisotropy measurements of TMA-DPH labeled cells. TMA-DPH bounds on the hydrophilic external surface of the cell membrane. The microwave irradiation of photoreceptor cells suspension was performed directly into the cuvette holder of the spectrofluorimeter using a coaxial cable. Fluorescence anisotropy was measured before, during and after microwave irradiation of cells suspension. (f = 2.45 GHz; irradiation time: 2 hours; power densities: μW- mW/cm2). It was observed that changes in the membrane fluidity depend on the power density used: irradiation at 5, 6 and 7 mW/cm2 leads to a decrease of cell membrane fluidity while irradiation at 1, 3, 8, 9 mW/cm2 shows no effect. Thus, it seems there is a power 'window' in the 5-7 mW/cm2 power range. The results are not due to the photoreceptor cells aging or to the internalization of TMA - DPH because we did also measurements using as controls rods labeled with TMA - DPH. In this case no change in fluorescence anisotropy was observed. The effects are transient, the membrane fluidity reverting to the initial values within 10 minutes after irradiation. The interaction mechanisms for μW and mW power domains seems to be different suggesting a power 'window' in the 5-7 mW/cm2 range. (authors)