Changes in cell proliferation due to environmental non-ionizing radiation: 2. Microwave radiation

Due to the use of mobile telephones, there is an increased exposure of the environment to weak radiofrequency (RF) electromagnetic fields, emitted by these devices. This study was undertaken to investigate if the microwave radiation from these fields will have a similar effect on cell proliferation as weak electromagnetic (ELF) fields. The field was generated by signal simulation of the Global System for Mobile communications (GSM) of 960 MHz. Cell cultures, growing in microtiter plates, were exposed in a specially constructed chamber, a Transverse Electromagnetic (TEM) cell. The Specific Absorption Rate (SAR) values for each cell well were calculated for this exposure system. Experiments were performed on cell cultures of transformed human epithelial amnion cells (AMA), which were exposed to 960 MHz microwave fields at three different power levels and three different exposure times, respectively. It was found that cell growth in the exposed cells was decreased in comparison to that in the control and sham exposed cells. Cell proliferation during the period following exposure varied not only with the various SAR levels, but also with the length of exposure time. On the other hand, repeated periods of exposure did not seem to change the effects. There was a general linear correlation between power level and growth change. However, the exposure time required to obtain the maximum effect was not the same for the various power levels. It turned out that at low power level, a maximum effect was first reached after a longer exposure time than at higher power level. A similar phenomenon was registered in the studies on ELF electromagnetic fields. Here, it was found that there was a linear correlation between the length of exposure time to obtain maximum effect and field strength.     

Local exposure of 849 MHz and 1763 MHz radiofrequency radiation to mouse heads does not induce cell death or cell proliferation in brain

Even though there is no direct evidence to prove the cellular and molecular changes induced by radiofrequency (RF) radiation itself, we cannot completely exclude the possibility of any biological effect of mobile phone frequency radiation. We established a carousel-type exposure chamber for 849 MHz or 1763 MHz of mobile phone RF radiation to expose RF to the heads of C57BL mice. In this chamber, animals were irradiated intermittently at 7.8 W/kg for a maximum of 12 months. During this period, the body weights of 3 groups-sham, 849 MHz RF, and 1763 MHz RF-did not show any differences between groups. The brain tissues were obtained from 3 groups at 6 months and 12 months to examine the differences in histology and cell proliferation between control and RF exposure groups, but we could not find any change upon RF radiation. Likewise, we could not find changes in the expression and distribution of NeuN and GFAP in hippocampus and cerebellum, or in cell death by TUNEL assay in RF exposure groups. From these data, we conclude that the chronic exposure to 849 MHz and 1763 MHz RF radiation at a 7.8 W/kg specific absorption rate (SAR) could not induce cellular alterations such as proliferation, death, and reactive gliosis.     

Effects of isothermal 2.45 GHz microwave radiation on the mammalian cell cycle: comparison with effects of isothermal 27 MHz radiofrequency radiation exposure

Synchronized Chinese hamster ovary (CHO) cells were exposed to continuous wave (CH) 2.45 GHz microwave radiation (MWR) or CW 27 MHz radiofrequency radiation (RFR) under isothermal conditions (37±0.2°) to test the following hypotheses: (1) high frequency electromagnetic radiation exposure directly affects the mammalian cell cycle in the absence of radiation-induced heating; and (2) the magnitude of the cell cycle alteration is frequency dependent. CHO cells in either G₀/G₁-, S−, or G₂/M-phase of the cell cycle were simultaneously exposed to CW 27 MHz RFR or CW 2.45 GHz MWR at specific absorption rates (SARs) of 5 or 25 W kg⁻¹, or sham exposed, at 37±0.2°C. Cell cycle alterations were determined by flow cytofluorometry over a 4 d period after exposure. The DNA distributions of RFR, MWR, and sham exposed cells were compared to detect qualitative effects on the cell cycle. Quantitative measures of the effects of isothermal radiation exposure were determined from differences in the number of exposed and sham exposed cells in various cell cycle phases as well as comparison of the mean DNA content of exposed and sham exposed cell samples. Flow cytofluorometric assay precision and accuracy were determined by comparison of DNA distributions of replicate CHO control cell samples and by the use of internal DNA standards.Exposure to 27 MHz RFR or 2.45 GHz MWR altered the CHO cell cycle for periods of up to 4 d following exposure at SARs of 5 or 25 W kg⁻¹. There were significant differences in temporal responses, cell cycle phase sensitivity, and overall degree of cell cycle alteration for 27 MHz compared with 2.45 GHz radiation exposure. In contrast to the effect of 27 MHz RFR, which did not affect G₂/M-phase CHO cells, 2.45 GHz MWR altered all cell cycle phases to varying degrees. Exposure to 2.45 GHz MWR at 5 or 25 W kg⁻¹ was twice as effective as 27 MHz RFR in inducing cell cycle alterations as determined by differences in the number of exposed versus sham-exposed cells in various cell cycle phases.     

Changes in cell proliferation due to environmental non-ionizing radiation 1. ELF electromagnetic fields

To study the effect of extremely low frequency (ELF) magnetic fields on cell growth, human cells (AMA cells) and K14 skin fibroblasts cells, growing in monolayer culture, were exposed to a sinusoidal 50 Hz, 80 μT field. Exposure times varied from 15 to 90 min. Changes in cell proliferation rates were then studied during subsequent field-free incubation, for 24 h.The results showed that a 30 min exposure resulted in a much higher increase in proliferation rates in the AMA cells compared with non-exposed cells or cells exposed to electromagnetic fields for shorter or longer times. The magnitude of the increase also depended on the initial proliferation rate and confluency. The exposure to varying field densities showed that the greatest increase in proliferation occurred at 80 μT.     

Microscopic observation of living cells during their exposure to modulated electromagnetic fields

Studying cell behaviour under irradiation with radiofrequency electromagnetic fields (RF-EMF) is often impeded by the difficulty to monitor cell characteristics during irradiation. Here we report the design and the application of a complete device for continuous microscopic observation of cells exposed to modulated EMF similar to mobile phones signals. The system allows the follow up of cell progression into mitosis under controlled temperature and CO(2) environment. Protocols are proposed in which the same cells are the controls before and after the EMF exposure and we demonstrate the interest of the "before exposure" controls. The exposure system was validated by cell endocytosis measurements. While the endocytosis rate was increased, no alteration of mitosis progression and mitosis duration was observed in cells exposed to 900 MHz modulated EMF for 1 h, at 30 degrees C and at a Specific Absorption Rate of 2.2 W/kg.     

The Effects of UV Emission from Compact Fluorescent Light Exposure on Human Dermal Fibroblasts and Keratinocytes In Vitro

Compact fluorescent light (CFL) bulbs can provide the same amount of lumens as incandescent light bulbs, using one quarter of the energy. Recently, CFL exposure was found to exacerbate existing skin conditions; however, the effects of CFL exposure on healthy skin tissue have not been thoroughly investigated. In this study, we studied the effects of exposure to CFL illumination on healthy human skin tissue cells (fibroblasts and keratinocytes). Cells exposed to CFLs exhibited a decrease in the proliferation rate, a significant increase in the production of reactive oxygen species, and a decrease in their ability to contract collagen. Measurements of UV emissions from these bulbs found significant levels of UVC and UVA (mercury [Hg] emission lines), which appeared to originate from cracks in the phosphor coatings, present in all bulbs studied. The response of the cells to the CFLs was consistent with damage from UV radiation, which was further enhanced when low dosages of TiO₂ nanoparticles (NPs), normally used for UV absorption, were added prior to exposure. No effect on cells, with or without TiO₂ NPs, was observed when they were exposed to incandescent light of the same intensity.     

Phlorotannin and antioxidant responses upon short-term exposure to UV radiation and elevated temperature in three south Pacific kelps

Rapid adjustments of the photosynthetic machinery and efficient antioxidant mechanisms to scavenge harmful ROS are physiologic adaptions exhibited by intertidal seaweeds to persist in temperate regions. This study examines short-term (3 h) responses of three large kelps from the cold-temperate coast of Chile, normally adapted to water temperatures <16°C, but exposed abruptly to simultaneous high temperatures and UV radiation during low tide in summer. The kelps were exposed in the laboratory to three temperatures (10, 20 and 28°C) with and without UV radiation, and photochemical reactions, concentration of phlorotannins and antioxidant activity were examined. The exposure to elevated temperature (slightly exacerbated by the presence of UV radiation) decreased photochemical processes (measured as fluorescence kinetics) in the three studied species and increased lipid peroxidation in two of them. The concentration of total soluble phlorotannins was variable and correlated with the antioxidant activity in the presence of UV radiation. Insoluble phlorotannins did not change during the exposure. In all, the downregulation of the photochemical machinery, which was expressed as dynamic photoinhibition, and the rapid induction of soluble phlorotannins triggered by UV radiation minimized the effects of oxidative stress and maintained the operation of photochemical processes during short-term thermal stress.     

Effect of ultraviolet-B radiation on intact cells of the cyanobacterium Spirulina platensis: characterization of the alterations in the thylakoid membranes

Intact trichomes of Spirulina platensis are exposed to ultraviolet- B (UV-B) radiation (270-320 nm; 1.9 mW m(-2)) for 9 h. This UV-B exposure results in alterations in the pigment-protein complexes and in the fluorescence emission profile of the chlorophyll-protein complexes of the thylakoids as compared with thylakoids isolated from control dark-adapted Spirulina cells. The UV-B exposure causes a significant decrease in photosystem II activity, but no loss in photosystem I activity. Although there is no change in the photosystem I activity in thylakoids from UV-B-exposed cells, the chlorophyll a emission at room temperature and at 77 K indicates alterations associated with photosystem I. Additionally, the results clearly demonstrate that the photosystem II core antennae of chlorophyll proteins CP47 and CP43 are affected by UV-B exposure, as revealed by Western blot analysis. Furthermore, a prominent 94 kDa protein band appears in the sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) profile of UV-B-exposed cell thylakoids, which is absent from the control thylakoids. This 94 kDa protein appears not to be newly induced by UV-B exposure, but could possibly have originated from the UV-B-induced cross-linking of the thylakoid proteins. The exposure of isolated Spirulina thylakoids to the same intensity of UV-B radiation for 1-3 h induces losses in the CP47 and CP43 levels, but does not induce the appearance of the 94 kDa protein band in SDS-PAGE. These results clearly demonstrate that prolonged exposure of Spirulina cells to moderate levels of UV-B affects the chlorophyll a-protein complexes and alters the fluorescence emission spectral profile of the pigment-protein complexes of the thylakoid membranes. Thus, it is clear that chlorophyll a antennae of Spirulina platensis are significantly altered by UV-B radiation.     

Melatonin prevents magnetic-field-induced neurite outgrowth in a subline of pheochromocytoma cells,PC12D

Exposure to extremely low frequency (ELF) magnetic fields (MFs) has been reported to affect several cellular processes, including cell growth and differentiation. Other research has demonstrated that the pineal gland and its hormone melatonin have a wide spectrum of effects in cells and organs and can exert modulatory actions on cell proliferation and cell differentiation. Since ELF electric and magnetic fields have been shown to influence pineal activity and melatonin synthesis and/or function, it has been suggested that some of the reported effects of ELF MFs could be a consequence of the direct action of these fields on the pineal gland and/or melatonin function. Possible interactions between MFs and melatonin effects are in an early stage of investigation. In this study, we have investigated the influence of melatonin on the in vitro response of a subline of pheochromocytoma cells, PC12D, to a MF. Cells were exposed to the combined action of a physiological concentration (10⁻¹⁰ M) of melatonin and a vertical, 50 Hz, 40 mG rms MF for 23 h. At the end of the treatment, the percentages of neurite-bearing cells were determined by microscopic examination and compared with those from samples treated with the field alone or with melatonin alone. MF exposure alone significantly increased the neurite outgrowth when compared with negative controls, supporting previous results by Blackman and coworkers; this effect was not observed when melatonin was present in the medium from the onset of the exposure. Although the mechanisms of action of melatonin and ELF MFs at the cellular level remain unknown, the present data suggest that physiological levels of melatonin can prevent PC12D cells from responding to the MF stimulus.     

In vitro survival of nonsmall cell lung cancer cells following combined treatment with ionizing radiation and photofrin-mediated photodynamic therapy

It has been suggested that combination high dose rate (HDR) intraluminal brachytherapy and photodynamic therapy (PDT) in nonsmall cell lung cancer (NSCLC) may improve efficacy of treatment, reduce toxicity and enhance quality of life for patients. To provide a cellular basis for this we examined the in vitro sensitivity of MRC5 normal lung fibroblasts and four NSCLC cell lines following HDR radiation, PDT and combined HDR radiation and PDT. HDR radiation was cobalt-60 gamma rays (1.5–1.9 Gy min⁻¹). For PDT treatment, cells were exposed to 2.5 μg mL⁻¹ Photofrin for 18–24 h followed by light exposure (20 mW cm⁻²). For combined treatment cells were exposed to Photofrin and then either exposed to light and 15–30 min later exposed to HDR radiation or exposed to HDR radiation and 15–30 min later exposed to light. D₃₇ values calculated from clonogenic survival curves indicated a six-fold difference in HDR radiation sensitivity and an eight-fold difference in PDT sensitivity. The effect of combined treatment was not significantly different from an additive effect of the individual treatment modalities for the NSCLC cells, but was significantly less than additive for the MRC5 cells. These results suggest an equivalent tumor cell kill may be possible at reduced systemic effects to patients.     

Effects of elevated temperatures during interruption of irradiation on Harwell Red 4034 PMMA and Kodak Biomax alanine film dosimetry systems

In the industrial setting it is not uncommon for a process interruption to occur during irradiation. In this event, dosimeters may be exposed to prolonged periods of elevated temperature without exposure to ionizing radiation. Once the process is restarted, the same dosimeters are exposed to ionizing radiation in order to achieve target dose. The goal of this experiment was to simulate a process interruption within limits and quantify the effects of a combination of factors (heat, time, and fractionation) on dosimeter response. We present an in-depth experimental study on the response of dosimeters that have been irradiated, stored for a fixed period of time at several temperatures, and then re-irradiated. This study was performed using Harwell Red 4034 polymethylmethacrylate (PMMA) and Kodak BioMax alanine film dosimeters.     

An animal model for extracorporeal photochemotherapy based on contact hypersensitivity.

Recently, photopheresis was introduced as a specific immune suppressor in several T cell mediated disorders. In order to study photopheresis, animal models are indispensable. This report describes an easy to handle model for this purpose. It concerns the Wistar-derived rat with contact hypersensitivity (CHS), also a T cell mediated disorder that has already been studied extensively in several other fields of research. After subsequent exposure to 8-methoxypsoralen (8-MOP) and ultraviolet A radiation (UVA), white blood cells from CHS rats were intravenously injected into other syngeneic rats suffering from the same disorder. This treatment appears to be very efficacious in suppressing the immunological response against the applied contact allergen, 2,4-dinitrofluorobenzene (DNFB). Cells subsequently exposed to UVA and 8-MOP did not have any effect.     

ISOLATION OF V79 FIBROBLAST CELL LINES CONTAINING ELEVATED METALLOTHIONEIN LEVELS THAT HAVE INCREASED RESISTANCE TO THE CYTOTOXIC EFFECTS OF ULTRAVIOLET-A RADIATION

Abstract Isolated clones of V79 Chinese hamster lung fibroblasts, selected for resistance against cadmium toxicity, were exposed to monochromatic 365 nm ultraviolet-A (UVA, 320 nm to visible light) radiation and examined for cell survival. All three of the Cd-resistant V79 clones (V79Cd) tested exhibited significant increases in survival after irradiation compared with control cultures similar to the increased survival observed in Zn acetate-induced V79 cells. Dose-modifying factors calculated for these survival experiments were all approximately 1.5. When characterized for steady-state levels of metallothionein (MT) mRNA and associated Cd-binding activity, all of the Cd-resistant V79Cd clones demonstrated elevated constitutive levels of both, implicating MT as the mechanism responsible for the observed cellular resistance to Cd and also to 365 nm UVA radiation. However, whereas levels of intracellular MT protein correlated with differences in survival against Cd, MT intracellular levels did not correlate well with protection against 365 nm UVA. Increased cell survival after exposure to 365 nm UVA radiation mediated by MT appeared to reach a threshold level and MT only provided a limited degree of protection. Since UVA radiation is known to cause cell death mediated through the intracellular generation of reactive oxygen species (ROS), these results suggest that the role of MT in ameliorating cellular photooxidative damage produced by UVA is by reducing intracellular ROS.     

Evidence for genotoxic effects of resonant ELF magnetic fields

The possibility that extremely low frequency (ELF) magnetic fields affect the genomic integrity of the cell is the objective of this study. Human peripheral lymphocytes (HPLs) were exposed to different exposure conditions combining ac and static magnetic fields. We used the micronuclei (MN) cytogenetic technique, because MN formation is considered as a marker of chromosomal damage produced by genotoxic agents.The first set of experiments were performed at 50 Hz, 150 μT rms and 32 Hz, 75 μT and 150 μT rms magnetic fields with the static geomagnetic field components nulled. No effects were detected using the MN test on HPL as an indicator for cellular genomic damage when the static magnetic field was nulled. Moreover, such exposure to an ac magnetic field does not appear to interfere with the action of a powerful genotoxic agent mytomicin-C (MMC), i.e. there was no synergistic effect.The second set of experiments were conducted exposing cells to 32 Hz, 150 μT and 75 μT rms, parallel to a 42 μT dc magnetic field. The 75 μT rms, 32 Hz exposure condition was chosen to maximize the resonance effect on Ca²⁺ according to parametric resonance theory. We found a statistically significant increase of MN for both exposure conditions. This experiment provides evidence for the genotoxic effects of resonant ELF magnetic fields in human lymphocytes.     

Thermomechanical behavior of a polyphenylquinoxaline

Crosslinking of linear poly[2,2′-(1,4-phenylene)-6,6′-bis(3-phenylquinoxaline)] (PPQ) by isothermal heat exposure in the temperature range between 425 and 490°C was investigated by means of torsional braid analysis. The change in glass transition temperature due to isothermal exposure was used as a kinetic parameter. In order to determine the effect of molecular weight and type of polymer chain ends, three PPQ samples were prepared that differed only in molecular weight and polymer chain endgroups. The apparent activation energy of isothermal crosslinking was independent of molecular weight and chain endings. Its value of 60 kcal/mole is the same as that for the thermal degradation of PPQ (determined by isothermal weight loss measurements). The rates of change of T_g at a particular temperature, however, are a function of both molecular weight (at least for these polymers that do not have a sufficiently high molecular weight) and the type of polymer chain ends. It was observed that isothermally crosslinked PPQ gave a higher break point in the TGA curve and also an increased char yield at 800°C than the linear precursor.     

Changes in matrix gene and protein expressions after single or repeated exposure to one minimal erythemal dose of solar-simulated radiation in human skin in vivo

Damage to the skin extracellular matrix (ECM) is the hallmark of long-term exposure to solar UV radiation. The aim of our study was to investigate the changes induced in unexposed human skin in vivo after single or repeated (five times a week for 6 weeks) exposure to 1 minimal erythemal dose (MED) of UV solar-simulated radiation. Morphological and biochemical analyses were used to evaluate the structural ECM components and the balance between the degrading enzymes and their physiologic inhibitors. A three-fold increase in matrix metalloproteinase 2 messenger RNA (mRNA) (P < 0.02, unexposed versus exposed) was observed after both single and repeated exposures. Fibrillin 1 mRNA level was increased by chronic exposure (P < 0.02) and unaltered by a single MED. On the contrary, a single MED significantly enhanced mRNA levels of interleukin-1alpha (IL-1alpha), IL-1beta (P < 0.02) and plasminogen activator inhibitor-1 (P < 0.05). Immunohistochemistry demonstrated a significant decrease in Type-I procollagen localized just below the dermal-epidermal junction in both types of exposed sites. At the same location, the immunodetected tenascin was significantly enhanced, whereas a slight increase in Type-III procollagen deposits was also observed in chronically exposed areas. Although we were unable to observe any change in elastic fibers in chronically exposed buttock skin, a significant increase in lysozyme and alpha-1 antitrypsin deposits on these fibers was observed. These results demonstrate the existence of a differential regulation, after chronic exposure compared with an acute one, of some ECM components and inflammatory mediators.     

Removing UV-A and UV-C radiation from UV-B fluorescent lamp emissions. Differences in the inhibition of photosynthesis in the marine alga Dunaliella tertiolecta using chromate versus cellulose acetate-polyester filters

Ultraviolet-B (UV-B; 280-320 nm)-emitting lamps unavoidably emit ultraviolet-A (UV-A; 320-400 nm) and ultraviolet-C (UV-C; <280 nm) radiation. Short-wavelength-blocking filters are generally used to limit the wave bands of UV under investigation. The widespread use of such filters means that all exposures to UV-B radiation will have a significant UV-A component. Therefore, the physiological effects unique to UV-B exposure are difficult to clearly isolate. This study presents a method to remove the UV-A and UV-C "contamination" using a liquid potassium chromate (K(2)CrO(4)) filter, thus allowing more direct assessment of the effects of UV-B exposure. Cultures of the green marine alga Dunaliella tertiolecta were grown in the absence of UV radiation. Sunlamps supplied the UV radiation for a 24 h exposure (solar radiation was not used in this study). The UV radiation was filtered either by the standard method (i.e. cellulose acetate (CA) with polyester = Mylar controls) or by a liquid filter of potassium chromate. Photosynthetic responses were compared. Major decreases in the ratio of variable to maximal fluorescence in dark-adapted cells and photosynthetic capacity were observed in CA-filtered cultures, whereas no change was observed in cells exposed to the same UV-B flux with the UV-A removed by K(2)CrO(4). The use of a CA filter with a Mylar control does not link results unequivocally to UV-B radiation. Such results should be interpreted with caution.     

Infrared-A Irradiation-induced Inhibition of Human Keratinocyte Proliferation and Potential Mechanisms

Infrared-A (IRA), which can penetrate deeply into the human skin, is a major component of solar radiation and is recognized to promote photoaging of human dermis. To our knowledge, however, the cellular and molecular consequences of human epidermis exposure to IRA have not been clarified. Thus, we investigated whether IRA inhibits the proliferation of normal human epidermal keratinocytes (NHEKs). IRA irradiation ed in cell cycle arrest at G1 and a dose-dependent reduction in the proliferation of NHEKs. We found that mechanistic target of rapamycin complex 1 (mTORC1) was initially inactivated during IRA irradiation due to the formation of stress granules (SGs), and this inactivation was maintained for at least 6 h after irradiation due to Akt dephosphorylation. Furthermore, repeated exposure of human skin equivalents to IRA led to marked thinning of the epidermal cell layer. In conclusion, IRA irradiation inhibits mTORC1 activity possibly through two molecular mechanisms involving SG formation in the early-phase and subsequent Akt dephosphorylation. This sequential mechanism seems to cause G1 cell cycle arrest and a reduction in cell proliferation, supporting the hypothesis that the decreased proliferation of basal keratinocytes that occurs during skin aging might be partly attributable to IRA radiation.     

Changes in neurite outgrowth but not in cell division induced by low EMF exposure: influence of field strength and culture conditions on responses in rat PC12 pheochromocytoma cells

The effects of low electromagnetic field (EMF) exposure (4.5-15.8 microT, 50 Hz AC) on neurite outgrowth and cell division in rat PC12 pheochromocytoma cells were examined. The study involved two separate experimental series in which culture conditions during exposure to the magnetic fields differed. In series 1 (14 experiments in which culture conditions were not strongly conducive to cell differentiation [15% serum]), exposure to 4.5-8.25 microT for 23 h significantly inhibited neurite outgrowth by 21.5 +/- 1.3% (by Manova, p = 0.003). In contrast, in series 2 (12 experiments in which culture conditions promoted cellular differentiation [4% serum]), exposure to 4.35-8.25 microT for 23 h significantly stimulated neurite outgrowth by 16.9 +/- 1.1% (by Manova, p = 0.009). Thus, in both series, exposure to a narrow range of low EMF has significant, but opposite effects on neurite outgrowth. Exposure to higher fields, 8.25-12.5 microT (series 1) and 8.25-15.8 microT (series 2) had no significant effect on neurite outgrowth. These data, when considered with other reports, suggest that neuronal differentiation can be altered by low level EMF exposure. While this may not be detrimental, it merits further research. At present, the reasons for the significant changes in neurite outgrowth being confined to the same narrow field strength are unclear. As stated above, culture conditions in series 2 were more conducive to cell differentiation than those in series 1. This is reflected in the lower number of cells in control samples in series 2, at the end of the 23-h incubation, than in series 1 (- 16.9 +/- 1.7%, p = 0.003). As the same numbers were plated in both series, the medium used in series 1 allows more of the PC12 cells to divide; this is consistent with some cells reverting to a non-neuronal adrenal chromaffin phenotype [L. Greene, A. Tischler. Establishment of a noradrenergic clonal line of rat adrenal pheochromocytoma cells which respond to nerve growth factor. Proc. Natl. Acad. Sci. U. S. A., 73 (1976) 2424-2426]. Exposure to both ranges of magnetic fields (4.35-8.25 and 8.25-15.8 microT) has no effect on cell division. Thus, there is no evidence in this study that there is a mitogenic effect arising from low EMF exposure.     

Vertical migration and motility responses in three marine phytoplankton species exposed to solar radiation

Diurnal vertical migration in the water column and the impact of solar radiation on motility were investigated in three marine phytoplankton species: Tetraselmis suecica, Dunaliella salina and Gymnodinium chlorophorum. Cells were exposed to solar radiation either in ultraviolet radiation (UVR, 280-400 nm) transparent Plexiglas tubes (45 cm length, 10 cm diameter) or in quartz tubes under three radiation treatments: PAB (280-700 nm), PA (320-700 nm) and P (400-700 nm). The three species displayed different behavior after exposure to solar radiation. Tetraselmis suecica was insensitive to UVR and under high solar radiation levels, cells accumulated preferentially near the surface. Exposure experiments did not indicate any significant changes in swimming speed nor in the percentage of motile cells after 5 h of exposure. On the other hand, D. salina was sensitive to UV-B displaying a significant decrease in swimming speed and percentage of motile cells after 2-3 h of exposure. Moreover, D. salina cells migrated deep in the water column when irradiance was high. The response of G. chlorophorum was in between that of the other two species tested, with a slight (but significant) decrease in swimming speed and percentage of motile cells in all radiation treatments after 5 h of exposure. While G. chlorophorum cells were more or less homogenously distributed in the water column, a slight (but significant) avoidance response to high radiation was observed at local noon, with cells migrating deep in the water column. Our data clearly indicate that these sub-lethal effects of solar radiation are species-specific and they might have important implications for the aquatic ecosystem.