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Membrane response to static magnetic fields: effect of exposure duration
1Department of Neurology, School of Medicine, State University of New York, Stony Brook 11794-8121.
Abstract:
The time-course for the reversible alteration in presynaptic membrane function associated with exposure to a 123 mT static magnetic field was examined in an attempt to help define the mechanism whereby these fields influence biomembranes. Miniature endplate potentials (MEPPs) were recorded in the isolated murine neuromuscular junction preparation, maintained at a temperature of 35.5 degrees C. A minimum field duration of 50 s was found to be necessary for MEPP inhibition, with the efficacy of the field in inducing further inhibition being a function of its duration, but only for periods up to 150 s. Longer durations were not associated with additional inhibition. The time required for MEPP frequency to return to baseline, following deactivation of the field, was found to be linear for field durations up to 150 s. At and above this limit, recovery time remained constant at 135 s. These findings are consistent with the slow reorientation of diamagnetic molecular domains within the membrane and suggest tight coupling to the mechanism responsible for neurotransmitter release. The limits on this effect are compatible with the mechanical constraints imposed by the membrane's cytoskeleton.
Insights
Static magnetic fields reversibly alter presynaptic membrane function. Exposure duration influences miniature endplate potential inhibition and recovery time, suggesting molecular reorientation within the membrane.
Area of Science:
- Neuroscience
- Biophysics
- Cellular Biology
Background:
- Static magnetic fields (SMFs) are increasingly prevalent, necessitating an understanding of their biological effects.
- Biomembrane function, particularly at nerve terminals, may be sensitive to external electromagnetic fields.
- The precise mechanisms by which SMFs influence neuronal signaling remain largely undefined.
Purpose of the Study:
- To investigate the time-course of functional changes in presynaptic membranes exposed to a 123 mT static magnetic field.
- To elucidate the underlying biophysical mechanisms responsible for SMF-induced alterations in neurotransmission.
- To determine the relationship between SMF exposure duration and the observed effects on synaptic function.
Main Methods:
- Utilized an isolated murine neuromuscular junction preparation.
- Recorded miniature endplate potentials (MEPPs) to assess presynaptic function.
- Applied a 123 mT static magnetic field for varying durations and monitored MEPP frequency and recovery.
Main Results:
- A minimum SMF exposure of 50 seconds was required to inhibit MEPPs.
- MEPP inhibition increased with exposure duration up to 150 seconds, with no further effect at longer durations.
- Recovery of MEPP frequency to baseline was linear with exposure up to 150 seconds, then plateaued at 135 seconds.
Conclusions:
- Findings support a model of slow diamagnetic molecular domain reorientation within the presynaptic membrane.
- This reorientation appears tightly coupled to the neurotransmitter release mechanism.
- The observed temporal limits suggest mechanical constraints imposed by the membrane's cytoskeleton.