Resting potential of excitable neuroblastoma cells in weak magnetic fields

Abstract

The mechanism by which static and low-frequency magnetic fields are transduced into biological signals responsible for reported effects on brain electrical activity is not yet ascertained. To test the hypothesis that fields can cause a subthreshold change in the resting membrane potential of excitable cells, we measured changes in transmembrane current under voltage clamp produced in SH-SY5Y neuroblastoma cells, using the patch-clamp method in the whole-cell configuration. In separate experiments, cells were exposed to static fields of 1, 5, and 75 G, to time-varying fields of 1 and 5 G, and to combined static and time-varying fields tuned for resonance of Na+, K+, Ca2+, or H+. To increase sensitivity, measurements were made on cells connected by gap junctions. For each cell, the effect of the field was evaluated on the basis of 100 trials consisting of a 5-s exposure immediately followed by a 5-s control period. In each experiment, the field had no discernible effect on the transmembrane current in the vicinity of zero current (- 50 mV voltage clamp). The sensitivity of the measuring system was such that we would have detected a current corresponding to a change in membrane potential as small as 38 microV. Consequently, if sensitivity of mammalian cells to magnetic fields is mediated by subthreshold changes in membrane potential, as in sensory transduction of sound, light, and other stimuli, then the ion channels responsible for the putative changes are probably present only in specialized sensory neurons or neuroepithelial cells. A change in transmembrane potential in response to magnetic fields is not a general property of excitable cells in culture.

Glutamate antagonists limit tumor growth

“…Glutamate can depolarize membranes and may lead to elevation of intracellular Ca 2ϩ in astrocytoma or neuroblastoma cells (33,34). The resting membrane potential ranges in tumor cells between Ϫ30 and Ϫ50 mV (35,36). Patch clamp recordings in neurons demonstrate that at such membrane potentials Mg 2ϩ block of NMDA channels is reduced and that AMPA channels become permeable to cations (37,38).…”

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

“…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). A variety of other MF-induced physiological effects indirectly suggests the involvement of the Ca 2ϩ signal pathway (20,37,55,68,72,76,80,96,98).…”

Extracellular currents alter gap junction intercellular communication in synovial fibroblasts

“…The 5Y cells were grown under the same conditions as the HIG-82 cells, except for the addition of dibutyryl cAMP (50 mM, Sigma, St. Louis, MO) to the growth media to produce the electrically excitable phenotype [Toselli et al, 1996]. We showed previously that 5Y cells were connected by gap junctions [Sonnier et al, 2000].…”

“…One possibility is that the EMFs produced analgesia by directly affecting the cells of the nervous system. However, EMFs did not alter the resting membrane potential in an in vitro model of an excitable cell [Sonnier et al, 2000], and it seems unlikely that the weak EMFs typically used in the pain studies could alter the properties of the ion channels that produce the action potential [King, 1999]. However, specialized neuroepithelial cells could mediate the effect of fields, as is the case in some elasmobranch and teleost fishes [Fessard, 1974;Kalmijn, 2000].…”