The osmolarity of the electroporation medium affects the transient expression of genes

During transfection on 5123 and FT02B hepatoma cells and NIH 3T3 fibroblast cells by electroporation, it was observed that the expression of the reporter gene and the viability of the cells was very sensitive to varying amounts of DNA solution added, despite a constant setting of voltage and capacity during electroporation. As few quantitative data are available that detail the extent to which the efficiency of electroporation is dependent on medium osmolarity, the following experiment was performed according to Potter et al., except that the complete procedure was done at room temperature which resulted in an increase of the specific activity of CAT by approximately 25%. The data clearly indicate that the use of hypotonic medium during electroporation has to be avoided.