Measurement and analysis of static magnetic fields that block action potentials in cultured neurons

Abstract

To characterize the properties of static magnetic fields on firing of action potentials (AP) by sensory neurons in cell culture, we developed a mathematical formalism based on the expression for the magnetic field of a single circular current loop. The calculated fields fit closely the field measurements taken with a Hall effect gaussmeter. The biological effect induced by different arrays of permanent magnets depended principally on the spatial variation of the fields, quantified by the value of the gradient of the field magnitude. Magnetic arrays of different sizes (macroarray: four center-charged neodymium magnets of approximately 14 mm diameter; microarray; four micromagnets of the same material but of approximately 0.4 mm diameter) allowed comparison of fields with similar gradients but different intensities at the cell position. These two arrays had a common gradient value of approximately 1 mT/mm and blocked > 70% of AP. Alternatively, cells placed in a field strength of approximately 0.2 mT and a gradient of approximately 0.02 mT/mm produced by the macroarray resulted in no significant reduction of firing; a microarray field of the same strength but with a higher gradient of approximately 1.5 mT/mm caused approximately 80% AP blockade. The experimental threshold gradient and the calculated threshold field intensity for blockade of action potentials by these arrays were estimated to be approximately 0.02 mT/mm and approximately 0.02 mT, respectively, In conclusion, these findings suggest that spatial variation of the magnetic field is the principal cause of AP blockade in dorsal root ganglia in vitro.

Cellular target of weak magnetic fields: ionic conduction along actin filaments of microvilli

“…A third group of reports describes an inhibition of Ca 2ϩ signaling by strong static MFs in GH3 cells (72) and retardation of metabolic activity in HL60 cells (74), as well as a block of action potentials by static MFs in cultured neurons (11). Similarly, stimulation of cells with MF frequencies apart from the active frequency windows has been shown to act as an inhibitor to prestimulated Ca 2ϩ signaling (87,95).…”

Quantitative Analysis of Unique Deposition Pattern of Submicron Fe3O4Particles Using Computer-Controlled Scanning Electron Microscopy

“…These results quantitatively show that the particle number and size were not spatially uniform within each cluster. Previous work showing the increased effect of a steep magnetic field gradient on increased neural action potentials (Cavopol et al 1995) suggests that the deposition of more particles toward the edge may be due to the effect of the steep magnetic field gradient in this area where magnets of opposite poles meet. Haverkort et al (2009) have shown that capture efficiency increases with decreasing drag force so that smaller particles will be collected preferentially in the areas of highest field strength.…”

“…Surfaces with opposite poles attract and adhere to each other, while like poles repel. The array of tightly packed small adjacent magnets have close interactions and consist of multiple and alternating magnetic poles that form a steep magnetic field gradient with an inhomogeneous maximum effective region (MER) between adjacent magnets of alternating polarity (Cavopol et al 1995;McLean et al 2001). Iron oxide (Fe 3 O 4 ) particles are paramagnetic (magnetically susceptible) and become nonpermanent magnets in the presence of an electromagnetic field (Jackson 1999).…”

Spontaneous Neocortical Activity and Cognitive Functions: A Neuron-Astroglial Bio-Magnetic and Self-Organized Process

“…Many experimental works have shown that static magnetic fields can modulate neuronal physiology (Azanza and Calvo, 2000;Azanza and del Moral, 1994;Cavopol et al, 1995;Coots et al, 2004;Liboff, 1979;Rosen, 2003;Trabulsi et al, 1996;Vargas et al, 2006;Wieraszko, 2000;Ye et al, 2004). Some passive membrane properties of neurones are affected by the exposure to weak static magnetic fields, increasing the magnitude of evoked action potentials and excitatory postsynaptic potentials (Ye et al, 2004).…”

“…Indeed, McLean and associates showed that it was the magnetic field gradient instead of the intensity, the parameter that greatly affected the firing of cultured neurones (Cavopol et al, 1995). In this regard, it has been shown that fast firing neurones (>17 spikes/s) isolated from the hippocampal formation of homing pigeons, clearly displayed a phasic increase in firing during different ambient magnetic field conditions (Vargas et al, 2006).…”