Threshold and limits of magnetic field action at the presynaptic membrane
Department of Neurology, School of Medicine, State University of New York at Stony Brook 11794-8121.Biochimica et Biophysica Acta (Impact Factor: 4.66). 08/1994; 1193(1):62-6. DOI: 10.1016/0005-2736(94)90333-6
The relationship of field intensity and exposure duration to the inhibitory effect of static magnetic fields on presynaptic membrane function was examined in order to further define the mechanism of action of these fields. Miniature endplate potentials (MEPPs) were recorded from the isolated murine neuromuscular junction, maintained at a temperature of 35.5 degrees C, during exposure to static magnetic fields of varying duration and intensity. Inhibition of MEPP generation correlated well with the product of the square of the flux density and exposure time. At lower product values the relationship was linear with an absolute flux density threshold of 37.9 mT. Higher product values were associated with deviation from linearity indicative of a limit on the extent of inhibition. These findings are consistent with the hypothesis that static magnetic fields induce a reorientation of diamagnetic molecular domains within the membrane but with a restriction on the degree of reorientation imposed by the membrane's cytoskeleton.
Article: TRACT OF THE RATS
- [Show abstract] [Hide abstract]
ABSTRACT: Voltage-activated calcium channel function was examined in cultured GH3 cells using the whole-cell patch clamp technique. Exposure to a 120 mT static magnetic field resulted in a slight reduction in the peak calcium current amplitude and shift in the current-voltage relationship. The most significant change was a slowing of the channel activation rate without any change in the inactivation rate. All changes in channel function were reversible, with return to pre-exposure values within 3 min after the field was turned off. These alterations in channel function were temperature-dependent. The present findings are consistent with a functional disruption of the intramembranous portion of the calcium channel by a magnetically induced membrane deformation.
- [Show abstract] [Hide abstract]
ABSTRACT: The effects of zero magnetic field on human VH-10 fibroblasts and lymphocytes were studied by the method of anomalous viscosity time dependencies (AVTD). A decrease of about 20% in the AVTD peaks was observed within 40 to 80 min of exposure of fibroblasts. This decrease was transient and disappeared 120 min after beginning of exposure. Similar kinetics for the effect of zero field was observed when cells were exposed 20 min and then kept at an ambient field. A 20% decrease of the AVTD peaks (p < 0.005 to 0.05) 40 to 70 min after 20 min exposure to zero field was reproduced in four independent experiments (out of four) with human lymphocytes from the same healthy donor. Contrary to the effects of zero field, irradiation of lymphocytes or fibroblasts with gamma-rays resulted in significant increase of the AVTD peaks immediately after irradiation. We concluded that zero field and gamma-rays caused hypercondensation and decondensation of chromatin, correspondingly. The effect of ethidium bromide served as a positive control and supported this conclusion. The effects of zero field on human lymphocytes were more significant in the beginning of G1-phase than in G0-phase. Thus, human fibroblasts and lymphocytes were shown to respond to zero magnetic field.
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.