摘要:

AbstractWe describe a new system for exposing cultured biological cells that have been plated on coverslips to strong electrostatic fields at magnitudes>103V/cm. Techniques are described that make use of mineral oil to render insignificant electrical conduction currents (total leakage current is<1.0 nA or<0.1 nA/coverslip), joule heating (<10−6W), or current‐induced magnetic fields (<10−13T) in regions inhabited by cells. The mineral oil also eliminates a reduction in the strength of the applied field, which otherwise can occur from increased electrode‐to‐medium impedance at the site of application. Thus the applied field is reliably specified in the vicinity of a cell membrane. Control and electrostatic field chambers are housed in a grounded metal incubator. Cylindrical mu‐metal shields can be used to reduce background magnetic fields in each chamber from 40 μT static and ∼ 1 μT ac to, respectively,<3 μT static and ∼ 100 nT ac. Contamination of cells by impurity atoms that may leach from electrodes was measured by atomic‐absorption spectrophotometry and found to be negligible. Stray magnetic‐ and electric‐field components within the incubator were measured, as were background fields around the laboratory

ISSN:0197-8462    

DOI:10.1002/bem.2250130202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have attempted to measure the electromotive forces (emfs) induced in human beings moving at a constant speed in a highly dense magnetic field. Experiments were initially conducted on a set of models, and then directly on human subjects. The models consisted of single circular loops of Tygon tubing (I.D., 0.635 cm; O.D., 0.9525 cm) filled with normal saline solution, with circumferences of 20, 40, 60, 80, and 100 cm. The models were connected to an amplifier via silver/silver‐chloride electrodes. Each saline loop was mounted on a movable platform, with the plane of the loop perpendicular to the platform's axis; the platform was enabled to move at known constant speeds into and out of the bore of a 1.89‐T magnet. The human subjects were then substituted for the saline loops, with the long axis parallel to the direction of motion, and with standard EKG electrodes placed at 180° successively on the ankle, calf, lower thigh, upper thigh, chest, and head. In all cases, for human subjects and models, the peak induced voltage was directly proportional to the speed of movement and the square of the circumference of the bounded cross‐sectional areas. Thus, for the saline loops, the correlation coefficient between induced voltage and circumference was .998, and for human subjects, .947. Under the loose assumption that for equal circumferences the bounded areas in human subjects were equal to those in the circular loops, the induced emfs in human subjects were consistently about 13% greater than those in the loops. At a mean speed of 1.18 m/s, the chest had a peak induced voltage of 260 mV, while the voltage at the ankle had a peak of 19.8 mV. The experimental data were used to estimate the corresponding induced‐current density at the pericardium, 17 mA/m2. We conclude for a human subject moving at constant speed along the body's long axis into a magnetic field that Faraday's law is closely followed for various cross‐sections of the body. Further, in those cases in which the magnetic field and its gradient are not well‐established, one can use saline‐filled loops to estimate approximate values of voltages induced in human subjects. © 1992

ISSN:0197-8462    

DOI:10.1002/bem.2250130203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractData are presented on ankle‐specific SARs and foot currents as a function of strengths of radio‐frequency electromagnetic fields encountered by operators of dielectric heaters. The determination of foot currents was based on near‐field exposures in which reactive coupling dominates, and which can result in substantial SARs in exposed workers. The operators were located less than one wavelength from—usually within one meter of—the dielectric heaters, which generated fields at frequencies from 6.5 to 65 MHz. At distances normally assumed by workers, maximal strengths of electric fields ranged from 104to 2.4 × 106V2/m2; maximal strengths of magnetic fields ranged from 5.0 × 10−3to 33.3 A2/m2. Currents through both feet to ground were measured while operators stood where they normally worked. Maximal currents ranged from 3 to 617 mA, rms. Nearly 27 percent of the dielectric heaters induced foot currents that exceeded the 200‐mA limit that has been proposed for a new ANSI C95.1 standard. Twenty percent of the heaters induced foot currents that exceeded 350 mA. SARs in ankles were calculated from foot currents, and they approximated 5 W/kg at 100 mA, 29 W/kg at 250 mA, and 57 W/kg at 350 mA. The maximal SAR in the ankle was ∼ 176 W/kg at 617 mA. © 19

ISSN:0197-8462    

DOI:10.1002/bem.2250130204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe use of the transcription autoradiographic method permits identification of nascent RNA chains directly on identifiable regions of Drosophila salivary gland chromosomes. Changes in transcriptional activity at 13 defined regions of the right arm of chromosome 3 (3R) were observed following 20‐min exposures of salivary glands to five different extremely low frequency (ELF) electromagnetic (EM) fields. Changes in translational patterns were also induced by the ELF EM fields in exposed cells. Differences included an increase in over‐all polypeptide synthesis as well as in the number of polypeptides resolved in cells exposed to EM fields. © 1992 Wiley‐Lis

ISSN:0197-8462    

DOI:10.1002/bem.2250130205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMicroelectrode and voltage‐clamp techniques were modified to record spontaneous electrical activity and ionic currents ofLymnea stagnalisneurons during exposure to a 900‐MHz field in a waveguide‐based apparatus. The field was pulse‐modulated at repetition rates ranging from 0.5 to 110 pps, or it was applied as a continuous wave (CW). When subjected to pulsed waves (PW), rapid, burst‐like changes in the firing rate of neurons occurred at SARs of a few W/kg. If the burst‐like irregularity was present in the firing rate under control conditions, irradiation enhanced its probability of occurrence. The effect was dependent on modulation, but not on modulation frequency, and it had a threshold SAR near 0.5 W/kg. CW radiation had no effect on the firing rate pattern at the same SAR. Mediator‐induced, current activation of acetyl‐choline, dopamine, serotonin, or gamma‐aminobutyric‐acid receptors of the neuronal soma was not altered during CW or PW exposures and, hence, could not have been responsible for the bursting effect. ©

ISSN:0197-8462    

DOI:10.1002/bem.2250130206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe 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. ©

ISSN:0197-8462    

DOI:10.1002/bem.2250130207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe possibility that weak, ac and dc magnetic fields in combination may affect binding equilibria of calcium‐ions (Ca2+) was investigated with two metallochromic dyes as calcium‐binding molecules: murexide and arsenazo III. Calcium‐dye equilibria were followed by measuring solution absorbances with a fiber‐optic spectrophotometer. A Ca2+‐arsenazo solution was also used indirectly to monitor the binding of Ca2+to calmodulin. Parallel, ac and dc magnetic fields were applied to each preparation. The ac magnetic field was held constant during each of a series of experiments at a frequency in the range between 50 and 120 Hz (sine wave) or at 50 pps (square wave) and at an rms flux density in the range between 65 and 156 μT. The dc magnetic field was then varied from 0 to 299 μT at 1.3 μT increments. The magnetic fields did not measurably affect equilibria in the binding of metallochromic dyes or calmodulin to Ca2+. © 1992 Wi

ISSN:0197-8462    

DOI:10.1002/bem.2250130208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn the course of a study on residential magnetic‐field exposure, some incidental data were obtained that bear on the issue of confounding of magnetic field exposure by social class. We have explored the possibility that the magnetic flux density of 50 Hz fields measured in Melbourne streets is correlated with a number of variables that index the socio‐economic status of the neighborhood. We have examined also for a correlation between field‐intensity levels and sums of some or all of the indicators, which were weighted to provide an overall score on socio‐economic status. Although some of the indexes were weakly, but significantly, correlated with environmental levels of magnetic fields, the combined indices were not. These results indicate that socio‐economic status is not likely to be a confounder in epidemiological studies of residential exposure to ELF magnetic fields in Melbourne. © 1992 Wiley

ISSN:0197-8462    

DOI:10.1002/bem.2250130209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0197-8462    

DOI:10.1002/bem.2250130201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY