Electrode Assemblies Used for Electroporation of Cultured Cells

Electroporation was initially developed for the introduction of DNA into cells which grow in suspension and was performed in a cuvette with two flat electrodes on opposite sides. Different configurations were subsequently developed for the electroporation of adherent cells in situ, while the cells were growing on nonconductive surfaces or a gold-coated, conductive support. We developed an assembly where the cells grow and are electroporated on optically transparent, electrically conductive indium-tin oxide (ITO). This material promotes excellent cell adhesion and growth, is inert and durable, and does not display spontaneous fluorescence, making the examination of the electroporated cells by fluorescence microscopy possible. The molecules to be electroporated are added to the cells and introduced through an electrical pulse delivered by an electrode placed on top of the cells. We describe several electrode and slide configurations which allow the electroporation of large numbers of cells for large-scale biochemical experiments or for the detection of changes in cell morphology and biochemical properties in situ, with control, nonelectroporated cells growing on the same type of ITO-coated surface, side by side with the electroporated ones. In a modified version, this technique can be adapted for the study of intercellular, junctional communication; the pulse is applied in the presence of a fluorescent dye, such as lucifer yellow, causing its penetration into the cells growing on the conductive half of the slide, and the migration of the dye to the nonelectroporated cells growing on the nonconductive area is microscopically observed under fluorescence illumination. An assembly is also described for the electroporation of sensitive cells without the use of an upper electrode.