Recent Research Highlights
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False color image of a Jurkat cell stainded with the dye Annine-6. The color coded intensity of the fluorescence emission is correlated to the transmembrane potential of the cell.
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Transmembrane voltage changes during nanosecond pulsed electric field exposure. As immediate response to the exposure to an electric field, membranes are charged like a capacitor. We believe that this initial mechanism forces cells to a physiological response that will allow us to modify cell functions depending on the parameters of the applied electric field. We therefore consider the understanding of the membrane charging processes crucial in the explanation of these "downstream" or secondary biological effects. As a result we are currently the only group in the world able to measure transmembrane voltage changes with a resolution of 5 ns. We used the system to study the change in the membrane potential of Jurkat cells in response to nanosecond pulsed electric fields for pulses with a duration of 60 ns and maximum field strengths of about 100 kV/cm (100 V/cell diameter). Membranes of Jurkat cells were stained with a fast voltage-sensitive dye, Annine-6, which has a subnanosecond voltage response time.
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A temporal resolution of 5 ns was achieved by the excitation of this dye with a tuneable laser pulse. The laser pulse was synchronized with the applied electric field to record images at times before, during and after exposure. When exposing the Jurkat cells to a pulse, the voltage across the membrane at the anodic pole of the cell reached values of 1.6 V after 15 nanoseconds, almost twice the voltage level generally required for electroporation. Voltages across the membrane on the side facing the cathode reached values of only 0.6 V in the same time period, indicating a strong asymmetry in conduction mechanisms in the membranes of the two opposite cell hemispheres. This small voltage drop of 0.6-1.6 V across the plasma membrane demonstrates that nearly the entire imposed electric field of 10 V/µm penetrates into the interior of the cell and every organelle.
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