Incorporation of macromolecules into cells and vesicles by low electric fields: Induction of endocytotic-like processes

The present study shows a very efficient incorporation of polysaccharides and β-galactosidase into membrane vesicles and cells by low pulsed electric fields of much lower amplitudes than the threshold electric field for electroporation. The electric induced uptake of dextran-FITC, in the range of 1-2000 kD, was observed in 85% of the cell population, while preserving the cells' viability. The uptake of P-galactosidase, induced by low electric fields, revealed a 30 fold increase in the enzyme's concentration in the cytosal in comparison with its concentration in the extracellular medium. The underlying mechanism of this uptake, based on the electric field induced endocytotic-like process, emerges from the following observations: (i) The uptake is not driven by metabolic energy, since we obtained the incorporation of macromolecules into membrane vesicles or cells at low temperatures; (ii) The formation of vesicle-like structures containing the macromolecules is displayed by confocal fluorescence microscopy, which reveals the existence of massive vesicle-like structures in the cytosol, following exposure to the pulsed electric field; (iii) The formation of vesicle-like structures is supported by the observed decrease in forward light scattering and the increase in side light scattering from single exposed cells.