Electroporation of adherent cells in situ for the introduction of nonpermeant molecules

Efficient electroporation of DNA and protein into confluent and differentiated epithelial cells in culture

Electroporation-mediated delivery of molecules is a procedure widely used for transfecting complementary DNA in bacteria, mammalian and plant cells. This technique has proven very efficient for the introduction of macromolecules into cells in suspension culture and even into cells in their native tissue environment, e.g. retina and embryonic tissues. However, in spite of several attempts to date, there are no well-established procedures to electroporate polarized epithelial cells adhering to a tissue culture substrate (glass, plastic or filter). We report here the development of a simple procedure that uses available commercial equipment and works efficiently and reproducibly for a variety of epithelial cell lines in culture.

Volume changes of isolated human K562 leukemia cells induced by electric field pulses

Electropermeabilization of immobilized human leukemia K562 cells was studied by measuring changes in cell volume. Such changes reflect mass transfer between the cell and external medium. Electropermeabilization was carried out in an isosmotic water-sorbitol medium with a range of electric field strengths from 500 to 800 V. cm(-1), corresponding to low-energy levels. Electroporation of the K562 cell membrane was found to provoke an inflow of sorbitol and a corresponding osmotic inflow of water and/or an outflow of intracellular solutes due to Fick diffusion. Such flows were found to involve the shrinkage, swelling, or rupture of K562 cells, depending on the characteristics of the electric field and of the physiological state of cells. The behavior of immobilized cells was observed during their exposure to the electric field. The response in immobilized cell volume corresponded with the theoretical pore size and pore opening time, permitting an explanation of the behavior of cell suspensions subject to electrical fields.

Electroporation-induced formation of individual calcium entry sites in the cell body and processes of adherent cells

Electroporation is a widely used method for introducing macromolecules into cells. We developed an electroporation device that requires only 1 microl of sample to load adherent cells in a 10-mm2 surface area while retaining greater than 90% cell survivability. To better understand this device, field-induced permeabilization of adherent rat basophilic leukemia and neocortical neuroblastoma cells was investigated by using fluorescent calcium and voltage indicators. Rectangular field pulses led to the formation of only a few calcium entry sites, preferentially in the hyperpolarized parts of the cell body and processes. Individual entry sites were formed at the same locations when field pulses were repeated. Before calcium entry, a partial breakdown of the membrane potential was observed in both polar regions. Based on our results, a model is proposed for the formation and closure of macromolecule entry sites in adherent cells. First, the rapid formation of a large number of small pores leads to a partial membrane potential breakdown in both polar regions of the cell. Second, over tens of milliseconds, a few entry sites for macromolecules are formed, preferentially in the hyperpolarized part of cell body and processes, at locations defined by the local membrane structure. These entry sites reseal on a time scale of 50 ms to several seconds, with residual small pores remaining open for several minutes.

Applications of electroporation of adherent cells in situ, on a partly conductive slide

Nontraumatic, simple, and reproducible procedures for the introduction of nonpermeant molecules into adherent mammalian cells by in situ electroporation are described. Cells are grown on a glass slide, half of which is coated with electrically conductive, optically transparent, indium-tin oxide. An electric pulse is applied in the presence of the molecules to be introduced, and their effect on the cellular phenotype can be observed. The cells growing on the nonconductive side of the slide do not receive any pulse and serve as controls. Careful adjustment of electric field strength can achieve the introduction of the molecules into essentially 100% of the cells, and this treatment causes no detectable disruption to cellular metabolism. This is applied in the presence of the fluorescent dye, Lucifer yellow, causing its penetration into the cells growing on the conductive half of the slide. The migration of the dye to the nonelectroporated cells growing on the nonconductive area is microscopically observed under fluorescence illumination.