DNA Vector Polyethyleneimine Affects Cell pH and Membrane Potential: A Time-Resolved Fluorescence Microscopy Study

Polyethyleneimine (PEI) is one of the very efficient nonviral vectors being developed and tested for artificial gene transfer into target cells. One of its serious limitations is the significant cytotoxicity of the large amounts of free PEI in the mixtures of DNA and PEI used for transfection. To further investigate the cellular effects of free PEI, we have analyzed the PEI-induced alterations of various cell parameters such as membrane heterogeneity and fluidity, cytoplasmic pH, and plasma membrane potential in a variety of cells such as Swiss 3T3 fibroblast, Chinese hamster ovary, insect cells SF9, plant cell line BY2, and Saccharomyces cerevisae. Fluorescence probes such as Nile red, SNARF-1, and cyanine dye DiSC₂(3), coupled with the technique of picosecond time-resolved fluorescence microscopy, were used in estimating the above-mentioned cell parameters. It was found that the cell membranes were largely unperturbed by PEI. However, the cytoplasmic pH showed an increase of 0.1–0.4 units when the cells were treated with PEI. The plasma membrane potential was found to be depolarized in S. cerevisae and Swiss 3T3 cells. These results suggest that the cytotoxic effects of PEI may partly originate from inhibition of regulation of cytoplasmic pH and plasma membrane potential. Further, it is proposed that the resultant cell alterations favors the transfection process.