Resting potential of excitable neuroblastoma cells in weak magnetic fields

The mechanism by which static and low-frequency magnetic fields are transdu ced into biological signals responsible for reported effects on brain elect rical activity is not yet ascertained. To test the hypothesis that fields c an cause a subthreshold change in the resting membrane potential of excitab le cells, we measured changes in transmembrane current under voltage clamp produced in SH-SY5Y neuroblastoma cells, using the patch-clamp method in th e 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 t o combined static and time-varying fields tuned for resonance of Na+, K+, C a2+, or H+. To increase sensitivity, measurements were made on cells connec ted 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 followe d 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 potent ial as small as 38 mu V. 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 io n channels responsible for the putative changes are probably present only i n specialized sensory neurons or neuroepithelial cells. A change in transme mbrane potential in response to magnetic fields is not a general property o f excitable cells in culture.