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J M Mullins

Publications and source records attributed to J M Mullins.

At least 19 recordsLinked to original sources
PubMed2000

Thresholds for electromagnetic field-induced hypoxia protection: evidence for a primary electric field effect.

We have recently reported that weak electromagnetic (EM) field exposure of chick embryos induces a response that can be used to protect against subsequent hypoxic insult. This work is continued here with an exposure response study using 20-min exposure to 60 Hz magnetic fields over a range of 2-10 microT. Once again, the biomarker used was induction of hypoxia protection. A sigmoidal response curve was found, with exposures to magnetic field strengths > or = 4 microT inducing maximum hypoxia protection (68% survival). We also attempted to determine whether the magnetic or induced electric component of the EM field was responsible for the observed protection. This was accomplished by making measurements with two different orientations of the magnetic fields (perpendicular and parallel to the major axis of the egg). Owing to the configuration of the embryo in the egg, the induced electric field at the embryo was lower when the magnetic field was parallel to the major axis even though the magnetic field strength was the same for each orientation. Exposure of the embryos to the parallel orientation resulted in a reduced protective response. An exposure-response curve generated for this orientation of the field also showed a more "drawn-out" appearance, consistent with the observed distribution of embryo positions within the egg. Our results suggest that the induced electric, not the applied magnetic field, plays a primary role in the protective effect observed in this chick embryo model.

Animals↗
PubMed2000

Electromagnetic field-induced protection of chick embryos against hypoxia exhibits characteristics of temporal sensing.

We previously studied the response of mammalian cultured cells to weak, 60 Hz-electromagnetic (EM) fields. Two time constants, similar to those observed in chemotaxis, were found to govern the cellular response to the field. We concluded that a system of temporal sensing, similar to that employed in chemotaxis by motile bacteria, was operative. We termed the shorter time (approximately 0.1 s) the "sensing" time, and the longer time (approximately 10 s) the "memory" time. To investigate the possibility that temporal sensing was a general property of EM field-cell interaction, the temporal properties of another EM field-induced effect was studied. The EM field-induced protection against the effects of extreme hypoxia was examined in chick embryos. Embryos were exposed to 60 Hz-magnetic fields, the amplitudes of which were regularly altered throughout the 20-min exposure. Alteration was accomplished either by turning the field off and on at regular intervals (1-50 s), or by introducing brief (10 or 100 ms), zero amplitude gaps, once each second, throughout exposure. When the field was turned on and off at 0.1 s intervals, the protective effect conferred by a constant field was lost. At progressively longer on/off intervals, protection was progressively restored, maximizing at intervals of 10-30 s. Gapping the magnetic field for 10 ms, each second of exposure conferred the same protection as that observed for an uninterrupted field, but gapping the field at 100 ms each second produced a significant reduction in protection. These data exhibit remarkable consistency with those obtained in similar temporal studies of the magnetic field-induced enhancement of ornithine decarboxylase activity in L929 fibroblasts. It appears that temporal sensing is a general feature of the EM field-cell interaction.

Animals↗
PubMed1999

Dose-response of electromagnetic field-enhanced ornithine decarboxylase activity.

Alteration of ODC activity in animals or cultured cells exposed to extremely low frequency electromagnetic fields, or to modulated microwave fields, has been documented by several laboratories. However, an evaluation of the dose-response relationship in these experiments has not been done. We examined ODC activity in L929 fibroblasts exposed for 4 h to 60 Hz magnetic fields of different amplitudes. Our results show a clear threshold response which could be fitted to a sigmoidal function, with the 50% point occurring at approximately 5 microT. This sigmoidal response is characteristic of biological responses which are governed by ligand-receptor binding, and has been previously observed in the incidence of magnetic-field induced morphological abnormalities in chick embryos. The implications of this study are discussed in terms of environmental exposures to EM fields.

Animals↗
PubMed1998

Fluorescence microscopy of etched methacrylate sections improves the study of mitosis in plant cells.

Etched sections of methacrylate infiltrated plant tissue [Gubler (1989) Cell Biol. Int; Rep., 13:137-145; Baskin et al. (1992) Planta, 187:405-413] offer many advantages over the more traditional squash technique of Wick et al. [(1981) J. Cell Biol. 89:685-690] for immunofluorescence microscopic investigation of the plant cytoskeleton, especially during mitosis. These advantages include: (1) unimpeded access of antibody probes, (2) confocal-like imaging without the expense of confocal equipment, (3) maintenance of organ architecture as well as intracellular structure, (4) the ability to independently examine separate focal planes with the same or multiple antibody(s) or other labelling compounds, and (5) the ability to archive unetched sections, polymerized or non-polymerized infiltrated tissue. In this paper examples of staining of various microtubule cytoskeletal and mitotic proteins are shown in a variety of methacrylate embedded plant tissues.

Antibodies, Monoclonal↗
PubMed1997

Role of modulation on the effect of microwaves on ornithine decarboxylase activity in L929 cells.

The effect of 835 MHz microwaves on the activity of ornithine decarboxylase (ODC) in L929 murine cell was investigated at an SAR of approximately 2.5 W/kg. The results depended upon the type of modulation employed. AM frequencies of 16 Hz and 60 Hz produced a transient increase in ODC activity that reached a peak at 8 h of exposure and returned to control levels after 24 h of exposure. In this case, ODC was increased by a maximum of 90% relative to control levels. A 40% increase in ODC activity was also observed after 8 h of exposure with a typical signal from a TDMA digital cellular telephone operating in the middle of its transmission frequency range (approximately 840 MHz). This signal was burst modulated at 50 Hz, with approximately 30% duty cycle. By contrast, 8 h exposure with 835 MHz microwaves amplitude modulated with speech produced no significant change in ODC activity. Further investigations, with 8 h of exposure to AM microwaves, as a function of modulation frequency, revealed that the response is frequency dependent, decreasing sharply at 6 Hz an 600 Hz. Exposure with 835 MHz microwaves, frequency modulated with a 60 Hz sinusoid, yielded no significant enhancement in ODC activity for exposure times ranging between 2 and 24 h. Similarly, exposure with a typical signal from an AMPS analog cellular telephone, which uses a form of frequency modulation, produced no significant enhancement in ODC activity. Exposure with 835 MHz continuous wave microwaves produced no effects for exposure times between 2 and 24 h, except for a small but statistically significant enhancement in ODC activity after 6 h of exposure. Comparison of these results suggests that effects are much more robust when the modulation causes low-frequency periodic changes in the amplitude of the microwave carrier.

Animals↗
PubMed1997

The role of temporal sensing in bioelectromagnetic effects.

Experiments were conducted to see whether the cellular response to electromagnetic (EM) fields occurs through a detection process involving temporal sensing. L929 cells were exposed to 60 Hz magnetic fields and the enhancement of ornithine decarboxylase (ODC) activity was measured to determine cellular response to the field. In one set of experiments, the field was turned alternately off and on at intervals of 0.1 to 50 s. For these experiments, field coherence was maintained by eliminating the insertion of random time intervals upon switching. Intervals < or = 1 s produced no enhancement of ODC activity, but fields switched at intervals > or 10 s showed ODC activities that were enhanced by a factor of approximately 1.7. These data indicate that it is the interval over which field parameters (e.g., amplitude or frequency) remain constant, rather than the interval over which the field is coherent, that is critical to cellular response to an EMF. In a second set of experiments, designed to determine how long it would take for cells to detect a change in field parameters, the field was interrupted for brief intervals (25-200 ms) once each second throughout exposure. In this situation, the extent of EMF-induced ODC activity depended upon the duration of the interruption. Interruptions > or = 100 ms were detected by the cell as shown by elimination of field-induced enhancement of ODC. That two time constants (0.1 and 10 s) are involved in cellular EMF detection is consistent with the temporal sensing process associated with bacterial chemotaxis. By analogy with bacterial temporal sensing, cells would continuously sample and average an EM field over intervals of about 0.1 s (the "averaging" time), storing the averaged value in memory. The cell would compare the stored value with the current average, and respond to the EM field only when field parameters remain constant over intervals of approximately 10 s (the "memory" time).

Animals↗
PubMed1997

Bioeffects induced by exposure to microwaves are mitigated by superposition of ELF noise.

We have previously demonstrated that microwave fields, amplitude modulated (AM) by an extremely low-frequency (ELF) sine wave, can induce a nearly twofold enhancement in the activity of ornithine decarboxylase (ODC) in L929 cells at SAR levels of the order of 2.5 W/kg. Similar, although less pronounced, effects were also observed from exposure to a typical digital cellular phone test signal of the same power level, burst modulated at 50 Hz. We have also shown that ODC enhancement in L929 cells produced by exposure to ELF fields can be inhibited by superposition of ELF noise. In the present study, we explore the possibility that similar inhibition techniques can be used to suppress the microwave response. We concurrently exposed L929 cells to 60 Hz AM microwave fields or a 50 Hz burst-modulated DAMPS (Digital Advanced Mobile Phone System) digital cellular phone field at levels known to produce ODC enhancement, together with band-limited 30-100 Hz ELF noise with root mean square amplitude of up to 10 microT. All exposures were carried out for 8 h, which was previously found to yield the peak microwave response. In both cases, the ODC enhancement was found to decrease exponentially as a function of the noise root mean square amplitude. With 60 Hz AM microwaves, complete inhibition was obtained with noise levels at or above 2 microT. With the DAMPS digital cellular phone signal, complete inhibition occurred with noise levels at or above 5 microT. These results suggest a possible practical means to inhibit biological effects from exposure to both ELF and microwave fields.

Animals↗
PubMed1994

Temporally incoherent magnetic fields mitigate the response of biological systems to temporally coherent magnetic fields.

We have previously demonstrated that a weak, extremely-low-frequency magnetic field must be coherent for some minimum length of time (approximately 10 s) in order to affect the specific activity of ornithine decarboxylase (ODC) in L929 mouse cells. In this study we explore whether or not the superposition of an incoherent (noise) magnetic field can block the bioeffect of a coherent 60 Hz magnetic field, since the sum of the two fields is incoherent. An experimental test of this idea was conducted using as a biological marker the twofold enhancement of ODC activity found in L929 murine cells after exposure to a 60 Hz, 10 microT rms magnetic field. We superimposed an incoherent magnetic noise field, containing frequencies from 30 to 90 Hz, whose rms amplitude was comparable to that of the 60 Hz field. Under these conditions the ODC activity observed after exposure was equal to control levels. It is concluded that the superposition of incoherent magnetic fields can block the enhancement of ODC activity by a coherent magnetic field if the strength of the incoherent field is equal to or greater than that of the coherent field. When the superimposed, incoherent noise field was reduced in strength, the enhancement of ODC activity by the coherent field increased. Full ODC enhancement was obtained when the rms value of the applied EM noise was less than one-tenth that of the coherent field. These results are discussed in relation to the question of cellular detection of weak EM fields in the presence of endogenous thermal noise fields.

Animals↗
PubMed1993

The role of coherence time in the effect of microwaves on ornithine decarboxylase activity.

Previously, we demonstrated the requirements for a minimum coherence time of an applied, small amplitude (10 microT) ELF magnetic field if the field were to produce an enhancement of ornithine decarboxylase activity in L929 fibroblasts. Further investigation has revealed a remarkably similar coherence time phenomenon for enhancement of ornithine decarboxylase activity by amplitude-modulated 915 MHz microwaves of large amplitude (SAR 2.5 W/kg). Microwave fields modulated at 55, 60, or 65 Hz approximately doubled ornithine decarboxylase activity after 8 h. Switching modulation frequencies from 55 to 65 Hz at coherence times of 1.0 s or less abolished enhancement, while times of 10 s or longer provided full enhancement. Our results show that the microwave coherence effects are remarkably similar to those observed with ELF fields.

Animals↗
PubMed1993

Analysis of spindle microtubule organization in untreated and taxol-treated PtK1 cells.

Taxol, a microtubule stabilizing agent, has been used to study changes in spindle microtubule organization during mitosis. PtK1 cells have been treated with 5 micrograms/ml taxol for brief periods to determine its effect on spindle architecture. During prophase taxol induces microtubules to aggregate, particularly evident in the region between the nucleus and cell periphery. Taxol induces astral microtubule formation in prometaphase and metaphase cells concomitant with a reduction in spindle length. At anaphase taxol induces an increase in length in astral microtubules and reduces microtubule length in the interzone. Taxol-treated telophase cells show a reduction in the rate of furrowing and astral microtubules lack a discrete focus and are arranged more diffusely on the surface of the nuclear envelope. In summary, taxol treatment of cells prior to anaphase produces an increase in astral microtubules, a reduction in kinetochore microtubules and a decrease in spindle length. Brief taxol treatments during anaphase through early G1 promotes stabilization of microtubules, an increase in the length of astral microtubules and a delayed rate of cytokinesis.

Animals↗
PubMed1993

Gene-specific modulation of RNA synthesis and degradation by extremely low frequency electromagnetic fields.

Pulse-labeling studies from our laboratory and others have shown that extremely low frequency (ELF) electromagnetic fields can produce a transient increase in gene transcription. In this study, the synthesis, degradation and processing, and steady state levels of specific RNA species during exposure to ELF radiation were determined in human leukemia HL-60 cells. The overall steady state RNA levels, assessed by continuous and equilibrium labeling with 3H-uridine, were not affected by ELF exposure. Northern blot analysis using probes specific for c-myc, beta-actin, and 45S ribosomal RNA gene products revealed that ELF did not alter the steady state levels of these RNAs. Examination of gene-specific transcription by a novel nuclease protection assay revealed that while ELF did not substantially alter the transcription rates for c-myc and beta-actin, transcription of the 45S ribosomal RNA gene was increased by 40-50%. To explain the observed increase in the synthesis of 45S ribosomal RNA without an associated increase in its steady state level, the degradation and processing of the ribosomal gene transcript in the presence and absence of an ELF field were followed by pulse-chase 3H-uridine labeling. This revealed that ELF radiation accelerated both the processing and degradation of the ribosomal RNA transcript. During ELF exposure, the half-life of the 45S ribosomal RNA was decreased from 115 min. to 85 min. These results show that ELF can selectively affect RNA levels by modulating either the transcription rate and/or RNA post-transcriptional processing and turnover.

Actins↗
PubMed1991

Effect of coherence time of the applied magnetic field on ornithine decarboxylase activity.

Skepticism over the possibility of weak electromagnetic fields affecting cell function exists because endogenous thermal noise fields are larger than those reported to cause effects. Four-hour exposure to a 55- or 65-Hz field approximately doubles the specific activity of ornithine decarboxylase (ODC) in L929 cells. To test the idea that the cell discriminates against this thermal noise because it is incoherent, partial incoherence was introduced into the applied field by shifting the frequency between 55- to 65-Hz at intervals of tau coh--delta tau where tau coh is a predetermined time interval and delta tau much less than tau coh varies randomly from one frequency shift to the next. To obtain the full ODC enhancement, coherence of the impressed signal must be maintained for a minimum of about 10s. For tau coh = 5.0s a partial enhancement is elicited, and at 1.0s there is no response. Unfortunately coherence times of this duration are too short to solve the thermal noise puzzle.

Animals↗
PubMed1991

Delineation of electric and magnetic field effects of extremely low frequency electromagnetic radiation on transcription.

The relative effects of the electric and magnetic field components of extremely low frequency electromagnetic radiation (ELF) on transcription were examined in human leukemia HL-60 cells. Delineation of the individual field contributions was achieved by irradiating cells in separate concentric compartments of a culture dish within a solenoid chamber. This exposure system produced a homogeneous magnetic field with a coincident electric field whose strength varied directly with distance from the center of the culture dish. Irradiation of HL-60 cells with sine wave ELF at 60 Hz and a field strength of 10 Gauss produced a transient increase in the transcriptional rates which reached a maximum of 50-60% enhancement at 30-120 minutes of irradiation and declined to near basal levels by 18 hours. Comparison of transcription responses to ELF of cells in different concentric compartments revealed that the transcriptional effects were primarily the result of the electric field component with little or no contribution from the magnetic field.

Cell Line↗
PubMed1991

Microwave exposure alters the expression of 2-5A-dependent RNase.

The effects of 2.45-GHz continuous-wave microwaves (SAR = 130 mW/g) on the expression of the interferon-regulated enzymes 2'-5'-oligoadenylate (2-5A) synthetase(s) and 2-5A-dependent endoribonuclease (RNase L) were studied in murine L929 cells. Cells growing as monolayers were removed from the substratum and placed in suspension culture for a 4-h sham or microwave exposure. The cells were returned to monolayer growth for 18 h, and then harvested and assayed to determine the amount of RNase L protein (via [32P]2-5A binding) and the specific activities of RNase L and 2-5A synthetase. Binding of radioactive 2-5A to RNase L for sham- and microwave-exposed samples was 14.5 and 36.4% above control, respectively (the microwave-exposed bound 19.0% more probe than the sham-exposed). The increases in 2-5A binding were accompanied by corresponding elevations of RNase L specific activity. In contrast, sham or microwave irradiation produced no alterations in 2-5A synthetase specific activity. No detectable differences were noted in the postexposure cell viability, plating efficiency, or proliferation rate. Also, there were no detectable differences in cell viability or plating efficiency between controls and cultures irradiated for 2 h when the temperature was simultaneously increased to above normal physiological limits (39 to 45 degrees C). The SAR (130 mW/g) and the power density (95 mW/cm2) used for the greater part of this study were nearly 20 times higher than the ANSI limit of 8 mW/g and 5 mW/cm2 for any 1 g of exposed human tissue.

2',5'-Oligoadenylate Synthetase↗