Effect of microtubule resonant frequencies on neuronal cells

Recent studies suggest that microtubules (MTs) and tubulin proteins exhibit resonant frequencies in the radiofrequency (RF) range. We hypothesize that exposing neurons to externally applied RF waves tuned to an intrinsic resonant frequency of MTs or tubulin could disrupt the natural signaling occurring in and around them, leading to neurophysiological changes. To test this hypothesis, we assembled custom exposure systems that allow stable RF exposures of cell cultures in a controlled environment (37°C, 5% CO₂, 95% humidity). We then exposed differentiated NG108-15 neuronal cells to RF waves tuned to selected resonance peaks for tubulin (91 MHz and 281 MHz) and for MTs (3.0 GHz) for 1 hr at a power density of 0.24 mW/cm² (SAR = 0.012, 0.087, and 0.53 mW/kg, respectively). We used fluorescence imaging of endogenous MTs and current-clamp electrophysiology to investigate changes following RF exposures compared to sham. The results from the imaging data show a clear difference in the localization of fluorescent MTs between the sham and the RF exposed neuronal cells. The sham cells exhibited more fluorescence in the neurite projections, whereas the RF exposed cells showed a more diffuse pattern, with a stronger fluorescence in the cell body. The electrophysiological results showed that resting membrane potentials of the RF exposed neuronal cells were more depolarized than those of the sham cells. Consequently, we observed spontaneous action potentials in the RF exposed cells, which were not present in the sham cells. Overall, our results suggest that exposing neurons to MTs or tubulin resonant frequencies might affect MTs normal behavior, leading to neurophysiological changes. However, to confirm the specificity of resonant frequency effect and validate this idea, studies investigating exposures to nonresonant frequencies and additional tubulin and MTs resonant frequencies are warranted.