Effect of Cooling On Cell Volume and Viability After Nanoelectroporation

Electric pulses of nanosecond duration (nsEP) are emerging as a new modality for tissue ablation. Plasma membrane permeabilization by nsEP may cause osmotic imbalance, water uptake, cell swelling, and eventual membrane rupture. The present study was aimed to increase the cytotoxicity of nsEP by fostering water uptake and cell swelling. This aim was accomplished by lowering temperature after nsEP application, which delayed the membrane resealing and/or suppressed the cell volume mechanisms. The cell diameter in U-937 monocytes exposed to a train of 50, 300-ns pulses (100 Hz, 7 kV/cm) at room temperature and then incubated on ice for 30 min increased by 5.6 +/- 0.7 μm (40-50%), which contrasted little or no changes (1 +/- 0.3 μm, <10%) if the incubation was at 37 °C. Neither this nsEP dose nor the 30-min cooling caused cell death when applied separately; however, their combination reduced cell survival to about 60% in 1.5-3 h. Isosmotic addition of a pore-impermeable solute (sucrose) to the extracellular medium blocked cell swelling and rescued the cells, thereby pointing to swelling as a primary cause of membrane rupture and cell death. Cooling after nsEP exposure can potentially be employed in medical practice to assist tissue and tumor ablation.