Plasma membrane charging of Jurkat cells by nanosecond pulsed electric fields
The initial effect of nanosecond pulsed electric fields (nsPEFs) on cells is a change of charge distributions along membranes. This first response is observed as a sudden shift in the plasma transmembrane potential that is faster than can be attributed to any physiological event. These immediate, yet transient, effects are only measurable if the diagnostic is faster than the exposure, i.e., on a nanosecond time scale. In this study, we monitored changes in the plasma transmembrane potential of Jurkat cells exposed to nsPEFs of 60 ns and amplitudes from 5 to 90 kV/cm with a temporal resolution of 5 ns by means of the fast voltage-sensitive dye Annine-6. The measurements suggest the contribution of both dipole effects and asymmetric conduction currents across opposite sides of the cell to the charging. With the application of higher field strengths the membrane charges until a threshold voltage value of 1.4–1.6 V is attained at the anodic pole. This indicates when the ion exchange rates exceed charging currents, thus providing strong evidence for pore formation. Prior to reaching this threshold, the time for the charging of the membrane by conductive currents is qualitatively in agreement with accepted models of membrane charging, which predict longer charging times for lower field strengths. The comparison of the data with previous studies suggests that the sub-physiological induced ionic imbalances may trigger other intracellular signaling events leading to dramatic outcomes, such as apoptosis.
KeywordsnsPEF Plasma membrane charging Membrane poration Real-time fluorescence imaging Annine-6
This study was funded by an AFOSR DOD MURI grant on “Subcellular Response to Narrow Band and Wide Band Radio Frequency Radiation” administered by Old Dominion University. We would also like to thank Peter Fromherz (Max Planck Institute for Biochemistry) and Bernd Kuhn (Max Planck Institute for Medical Research) for their valuable advice and assistance in discussions regarding the Annine-6 dye.
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