Direct plasma stimuli including electrostimulation and OH radical induce transient increase in intracellular Ca²⁺ and uptake of a middle-size membrane-impermeable molecule

Despite the promising potential of medical treatments based on non-equilibrium atmospheric-pressure plasma, most of the underlying mechanisms remain unknown. Here we report that direct plasma irradiation (DPI) can induce transient increase in intracellular calcium (Ca²⁺) concentrations, thereby playing key roles in many cellular processes as well as the uptake of middle-size membrane-impermeable molecules, which did not occur with indirect plasma irradiation (IPI). Experimental measurements using a Pockels voltage probe and gelling chemical reagent showed that electric field of 150 kV/cm and hydroxyl radical (OH) supply to cell cultures were induced by DPI under a typical condition compared with IPI. In addition, significant inhibition of the OH scavenger D-mannitol indicated involvement of OH in those DPI-induced cellular responses. These results facilitate the elucidation of plasma-cell interaction and the development of plasma devices for medical treatments.