Electroporation Dependence on Cell Size: Optical Tweezers Study

Abstract

Electropermeabilization or electroporation is the electrical disruption of a cell's membrane to introduce drugs, DNA/RNA, proteins, or other therapies into the cell. Despite four decades of study, the fundamental science of the process remains poorly understood and controversial. We measured the minimum applied electric field required for permeabilization of suspended spherical cells as a function of the cell radius for three cell lines. Key to this work is our use of optical tweezers to precisely position individual cells and enable well-defined, repeatable measurements on cells in suspension. Our findings call into question fundamental assumptions common to all theoretical treatments that we know of. It is generally expected that, for individual cells from a particular cell line, large cells should be easier to electroporate than small ones: the minimum electric field to cause electropermeabilization should scale inversely with the cell diameter. We found instead that each cell line has its own characteristic field that will, on average, cause permeabilization in cells of that line. Electropermeabilization is a stochastic process: two cells which appear identical may have different permeabilization thresholds. However, for all three cell lines, we found that the minimum permeabilization field for any given cell does not depend on its size.

Recent advances in microfluidic techniques for single-cell biophysical characterization

“…Under the same uniform electrical field, the effective voltage across the cell membrane is a function of cell diameter. 64 Hence, cells with larger diameters are exposed to higher voltages and are more easily porated. In addition, the plasma membrane of different cell types (e.g., metastatic tumor cells vs. non-metastatic tumor cells) can possess different poration properties.…”

Micro-/nanofluidics based cell electroporation

“…1(e)). 46,59 In these single cell electroporation experiments, the to-be-delivered reagents and the intracellular compartments were often labeled with fluorescence probes so that intracellular trafficking could be conveniently tracked.…”

“…55,59 In some studies, low molecular weight fluorescence dyes, such as propidium iodide (PI) and YOYO, were used as indicator regents for cell membrane permeabilization (these fluorescent dyes are membraneimpermeable to normal cells) as shown in Fig. 1(f).…”

Cell-cell proximity effects in multi-cell electroporation

“…Cell manipulation was accomplished using an optical tweezers (more information can be found in our earlier paper 15 ). Typically, 300-400 mW of 1064 nm laser power was used to trap individual cells.…”

“…This work has been summarized in an earlier paper. 15 Additionally, that paper describes several experimental checks on the reliability of our experimental approach. Three important conclusions of that work are (I) the permeabilization threshold electric field does not depend on cell size; (II) the measured threshold poration field of a cell is not affected by the history of earlier poration attempts at lower voltages-to the accuracy of our measurements; (III) the optical tweezers have no impact on the measured poration threshold.…”