Electrophysiological search for magnetic field influence on ion channel gating in N1E-115 neuroblastoma cells
Description
The N1E-115 neuroblastoma cell line was developed as an electrophysiological model to search for effects of transient magnetic fields, mediated by the magnetic force, on conductance of voltage-gated ion channels A magnetic stimulator similar to those used for neuronal stimulation in clinical neurophysiology was designed and constructed. This device generates magnetic fields to 3.0 Tesla with a zero-to-peak time of 84 $\mu$s. A coil assembly mounted in the nose of an inverted stage microscope applied pulsed magnetic fields while cellular ionic currents were studied using the voltage-clamp technique A new procedure was developed to detect transient differences in ionic current to brief stimuli. A 'two-pulse' paradigm is employed in which a short voltage step is applied. After recovery from channel inactivation, an identical voltage step is applied with a concurrent magnetic pulse. After subtraction of the magnetic stimulus artifact, the current response to the first voltage step is subtracted from that of the second. Integration of this current difference represents the charge transfer across the membrane attributable to the magnetic stimulus. Differences in current as small as 1% can be successfully detected. Sensitivity of this test arises from the use of a paired control voltage step. This precludes the need for a priori knowledge of the current characteristics as with population-based measurements Transmembrane sodium current was found to decrease (X = $-$0.136 nC per nA of total transmembrane current, p $<$ 0.01) during magnetic stimulation when the membrane potential was biased near the point of maximal channel activation. This finding is consistent with electromagnetic gating theory in which channel conductance is decreased by hinderance between the channel's ion selectivity filter and the magnetic field-induced spiral course of ions passing through the channel. Potassium and calcium currents were unaffected