Magnetofection is a gene targeting technology that uses magnetic iron oxide nanoparticles (MNPs) to enhance vector delivery to target cells through application of a magnetic field. It is suitable for viral and non-viral gene delivery. We have recently established a cell culture of primary cortical neurons from mice that have been genetically engineered using DNA-tagged MNPs. This technique could prove to be useful in establishing genetically modified primary neurons that could promote repair following transfer into sites of injury or degeneration in the central nervous system. To assess whether this type of transfection altered neuronal electrical properties, we have carried out an electrophysiological characterisation of the sodium and potassium currents in these neurons, comparing transfected with non-transfected groups. Cortical primary neurons were harvested from embryonic mouse brains (E18, CD1) and cultured for 7 days at 37oC (5% CO2 / 95% O2) in Neurobasal-B27 supplemented medium without serum at a density of 60×103/cm2. MNPs (3.5 μl, mean diameter 160 nm, Neuromag) were complexed with 1 μg DNA (pMAX-GFP, green fluorescent protein) and exposed to neurons for 24 hours on day 7. During this time a magnetic field was applied (4 Hz, 30 min) to promote MNP uptake. When examined under blue excitation light, GFP+ cells exhibited strong green fluorescence in both cell soma and processes. Neurons were whole cell patch clamped at 20oC in neurobasal medium. The intracellular (pipette) solution contained (mM): KCl 140, MgCl2 3.5, Na2ATP 2.5, EGTA 1, HEPES 10, pH 7.4. We found voltage-dependent sodium currents and potassium currents in nearly all neurons studied (two neurons had no clear sodium currents and were excluded from the analysis). A 50 ms voltage clamp step from the holding potential (-60 or -70 mV) to voltages between -40 mV and 0 mV induced a rapidly activating inward sodium current followed by a more slowly activating outward potassium current. We compared sodium and potassium current amplitudes at -30 mV and 0 mV respectively in both groups. Sodium currents were -233 ± 58 pA and -313 ± 96 pA in GFP+ (n = 9) and GFP- (n = 7) groups respectively. Potassium currents were 755 ± 198 pA (GFP+, n = 9) and 787 ± 215 pA (GFP-, n = 7) (mean ± SEM). These means were not significantly different (T-test, p > 0.05). The sodium currents were completely blocked by short (0.7 s) focal applications of 25 µM tetrodotoxin. In some of these cells we examined spiking behaviour in current clamp, and found small action potentials (20-30 mV) in both groups in response to depolarising current steps from -50 mV. We conclude that transfection with GFP via MNP uptake does not significantly alter the sodium and potassium currents in these neurons.