Fiber-optic-guided near-infrared laser exposure induces depolarization of cultured primary sensory neurons and modifies biophysical properties of human Nav1.5 channels

Photobiomodulation, a therapeutic method promoting wound healing, reduction in inflammation, pain and apoptosis, was widely tested in neurological/psychiatric disorders. In Parkinson's disease positive results have been obtained recently by transcranial or deep-fiber-optic-based near-infrared (NIR) light application. We assessed the effects of NIR stimulation with a 808.5 nm diode laser applied via a multimode fiber with a sharp tip placed over the cell on enzyme-dissociated cultured adult rat primary sensory neurons and human embryo kidney (HEK293) cells stably expressing human voltage-dependent Na⁺ channels (Nav1.5) approached via patch-clamp. For each type of cell, specific series of voltage- or current-clamp protocols were applied initially and after 3 min of laser exposure or control conditions. Laser exposure induced in neurons a resting potential depolarization (6.6 ± 1.8 mV vs. 2.4 ± 1.8 mV in control, mean ± SEM, p = 0.0594). In Nav1.5-expressing cells, peak I_Na amplitude slightly increased after laser application (111.2 ± 14.9 % vs. 70.6 ± 10.4 % in control experiments), and in outside-out patches the differences were larger (96.64 ± 5.25 %-laser vs. 37.95 ± 9.14 %-control). Via chemiluminometry we evidenced a delayed increase in ATP production in laser-exposed HEK293 cells. An explanation of these effects is that NIR exposure facilitates ATP production, maintaining an adequate state of Na⁺ channels phosphorylation, but we cannot exclude direct polarization effects on macromolecules including ion channels produced by the intense oriented electric field of the laser beam.