Effect of cell size and shape on single-cell electroporation

Abstract

Single-cell electroporation was performed using electrolyte-filled capillaries on fluorescently labeled A549 cells. Cells were exposed to brief pulses (50-300 ms) at various cell-capillary tip distances. Cell viability and electroporation success were measured. In order to understand the variability in single-cell electroporation, logistic regression was used to determine whether the probabilities of cell survival and electroporation depend on experimental conditions and cell properties. Both experimental conditions and cell properties (size and shape) have a significant effect on the outcome. Finite element simulations were used to compare bulk electroporation to single-cell electroporation in terms of cell size and shape. Cells are more readily permeabilized and are more likely to survive if they are large and hemispherical as opposed to small and ellipsoidal with a high aspect ratio. The dependence of the maximum transmembrane potential across the cell membrane on cell size is much weaker than it is for bulk electroporation. Observed survival probabilities are related to the calculated fraction of the cell's surface area that is electroporated. Observed success of electroporation is related to the maximum transmembrane potential achieved.

Figure 1

Schematic diagram of the experimental setup. Cultured cells were mounted in a chamber on the microscope stage. The tapered outlet end of the capillary was positioned close to a fluorescent cell with the help of a micromanipulator. The inlet end of the capillary was placed in a buffer-filled vial. The setup was connected to a high voltage power supply.

Figure 2

Contour plots of probabilities of cell survivability and electroporation success as a function of pulse duration and cell-capillary tip distance and cell properties. The cell size changes in the horizontal direction. Cell sizes used were: small (5^th percentile; diameter 19 μm), median (50^th percentile; diameter 25 μm), and large (95^th percentile; diameter 39 μm). Aspect ratio changes in the vertical direction. Aspect ratio was changed from 1−3. Black grid marks the area of 0−50 % electroporation success. Red grid marks the area of 0−50 % cell survivability. Green grid marks the area of > 50 % electroporation success and > 50% cell survivability. Blue grid marks the area of > 90 % electroporation success and > 90 % cell survivability.

Figure 3

Simulated transmembrane potential (TMP) for three cell sizes (side view): small (5^th percentile; diameter: 19 μm), median (50^th percentile; diameter: 25 μm), and large (95^th percentile; diameter: 39 μm).

Figure 4

Maximum transmembrane potential (TMP_max) plotted as a function of distance for a small (5^th percentile; diameter: 19 μm), median (50^th percentile; diameter: 25 μm), and a large (95^th percentile; diameter: 39 μm) cell.

Figure 5

Cell area above the critical transmembrane potential (A*) plotted as a function of distance for a small (5^th percentile; diameter: 19 μm), median (50^th percentile; diameter: 25 μm), and a large (95^th percentile; diameter: 39 μm) cell.

Figure 6

Fraction of the cell area above a critical transmembrane potential (F*) plotted as a function of distance for a small (5^th percentile; diameter: 19 μm), median (50^th percentile; diameter: 25 μm), and a large (95^th percentile; diameter: 39 μm) cell.