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Biomedical subjects

M T Marron

Publications and source records attributed to M T Marron.

12 recordsLinked to original sources
PubMed2003

Effects of starvation and desiccation on energy metabolism in desert and mesic Drosophila.

Energy availability can limit the ability of organisms to survive under stressful conditions. In Drosophila, laboratory experiments have revealed that energy storage patterns differ between populations selected for desiccation and starvation. This suggests that flies may use different sources of energy when exposed to these stresses, but the actual substrates used have not been examined. We measured lipid, carbohydrate, and protein content in 16 Drosophila species from arid and mesic habitats. In five species, we measured the rate at which each substrate was metabolized under starvation or desiccation stress. Rates of lipid and protein metabolism were similar during starvation and desiccation, but carbohydrate metabolism was several-fold higher during desiccation. Thus, total energy consumption was lower in starved flies than desiccated ones. Cactophilic Drosophila did not have greater initial amounts of reserves than mesic species, but may have lower metabolic rates that contribute to stress resistance.

Animals↗
PubMed1995

Effects of electromagnetic fields on molecules and cells.

Evidence suggests that cell processes can be influenced by weak electromagnetic fields (EMFs). EMFs appear to represent a global interference or stress to which a cell can adapt without catastrophic consequences. There may be exceptions to this observation, however, such as the putative role of EMFs as promoters in the presence of a primary tumor initiator. The nature of the response suggests that the cell is viewing EMFs as it would another subtle environmental change. The age and state of the cell can profoundly affect the EMF bioresponse. There is no evidence that direct posttranscription effects occur as a result of EMF exposure. Although transcription alterations occur, no apparent disruption in routine physiological processes such as growth and division is immediately evident. What is usually observed is a transient perturbation followed by an adjustment by the normal homeostatic machinery of the cells. DNA does not appear to be significantly altered by EMF. If EMF exposure is associated with an increased risk of cancer, the paucity of genotoxic effects would support the suggestion that the fields act in tumor promotion rather than initiation. The site(s) and mechanisms of interaction remain to be elaborated. Although there are numerous studies and hypotheses that suggest the membrane represents the primary site of interaction, there are also several different studies showing that in vitro systems, including cell-free systems, are responsive to EMFs. The debate about potential hazards or therapeutic value of weak electromagnetic fields will continue until the mechanism of interaction has been clarified.

Animals↗
PubMed1994

Magnetic fields after translation in Escherichia coli.

Quantitative two-dimensional gel electrophoresis of proteins in E. coli exposed for 60 min to weak, pulsed magnetic fields (1.5 mT peak) show that numerous proteins are both increased and decreased by a factor of 2 or more. An increase in the levels of two proteins, the a subunit of DNA-dependent RNA polymerase and NusA, was confirmed by Western blot analysis.

Bacterial Proteins↗
PubMed1993

Altered protein synthesis in a cell-free system exposed to a sinusoidal magnetic field.

This report describes a new approach for examining weak extremely low frequency (ELF) electric and magnetic field interactions with living systems that exploits a cell-free transcription/translation system derived from Escherichia coli. Using two-dimensional polyacrylamide gel electrophoresis we previously had determined that the level of the alpha subunit of RNA polymerase in intact E. coli was elevated by exposure to weak ELF magnetic fields. In this paper, plasmids containing the alpha, or both the beta,beta' subunits of the RNA polymerase from E. coli were placed into a cell-free expression system. When this transcription/translation system was exposed to a 72-Hz sinusoidal magnetic field in the range 0.07 to 1.1 mT (rms) for periods of 5 min to 1 h, expression was enhanced. Weaker fields must be applied longer to produce an effect. For 10 min of field exposure, the threshold for an effect is 0.1 mT. These experiments demonstrate that an intact membrane is not an absolute requirement for transducing magnetic bio-effects.

Cell-Free System↗
PubMed1988

Low frequency electric and magnetic fields have different effects on the cell surface.

There is a considerable controversy over the nature of weak electromagnetic-field effects in living organisms. Part of the controversy can be traced to a lack of understanding of whether electric or magnetic fields are involved in producing bioeffects. We find that both 60 Hz electric and magnetic fields alter the cell surface of Physarum polycephalum. Exposure to electric fields increases the negative charge on the cell surface while magnetic-field exposure decreases the hydrophobic character of the surface. These effects appear to be additive and independent of the waveform of the applied fields.

Cell Membrane↗
PubMed1986

Pulsed magnetic fields alter the cell surface.

Pulsed magnetic fields (PMFS) are routinely used in the medical community to facilitate bone repair in clinical cases of non-union or pseudarthoses [(1984) Orth. Clin. No. Am. 15, 61-87]. Although this therapeutic regimen appears to be reasonably effective, the mechanism of action between specific PMFs and the target tissue remains unknown. Adding urgency to the need to understand the mechanism are a wide number of reports that have appeared which demonstrate that PMFs similar to those in clinical use can alter many basic physiological functions. We report that a 24 h exposure to PMFs alters the cell surface of Physarum polycephalum amoebae. Further, using the technique of aqueous two-phase partitioning, we present evidence for individual magnetic and electric field, cell surface effects.

Cell Membrane↗
PubMed1986

Effects of sinusoidal 60-Hz electric and magnetic fields on ATP and oxygen levels in the slime mold, Physarum polycephalum.

We have previously reported that exposing the vegetative plasmodia stage of Physarum polycephalum to either individual or simultaneously applied electric and magnetic fields (45-75 Hz, 0.14-2.0 G, and 0.035-0.7 V/m) lengthens their mitotic cycle, depresses their rate of reversible shuttle streaming, and lowers their respiration rate. In this article we report the effects of simultaneously applied electromagnetic fields (60 Hz, 1.0 G, 1.0 V/m), electric fields only (60 Hz, 1.0 V/m), magnetic fields only (60 Hz, 1.0 G) on the haploid amoeba of Physarum exposed for 120-180 days. Statistically significant depressions (about 8-11%) in ATP levels were observed with all field conditions; however, respiration was significantly decreased only when amoebae were subjected to either combined fields or electric fields alone. Magnetic fields alone failed to induce a significant decrease in respiration.

Adenosine Triphosphate↗
PubMed1982

Magnetic field effects on mitotic cycle length in Physarum.

Large plasmodia of Physarum polycephalum were formed from mixtures of micro-plasmodia grown in shaker cultures exposed to 2.0 G (rms), 75 Hz magnetic fields and non-exposed, control cultures. The exposed cultures had been grown continuously in the field and displayed a longer mitotic cycle than the controls. Mixed cultures display synchronous mitosis and a cycle length intermediate to the cycle lengths of exposed and control cultures. The cycle length of mixed cultures varied with the proportions of the mixture in a non-linear manner. The results are discussed in terms of several models.

Kinetics↗