Abstract
Because of the many potential applications in cell membrane research, genetic mapping and somatic hybridization (e.g., production of hybridoma cells), the development of techniques for in vitro cell fusion is receiving ever increasing attention [l-5]. However, cell fusion induced by the usual means (e.g., glycerol-monooleate, polyethylene glycol, Sendai virus), suffers from several disadvantages, i.e., unphysiological conditions, lack of control of the fusion process under the microscope, large variability in the number of cells subjected to fusion, low yield of fused cells, loss of intracellular components and limited viability. A new method for cell-to-cell fusion based on electrical breakdown in the membrane contact zones of two cells attached to each other has been introduced [6-14]. This method eliminates most of the disadvantages of the chemical- and virus-induced fusion techniques. Electric field-induced cell-to-cell fusion is performed in two steps. 1) Tight membrane contact between cells is achieved by dielectrophoresis [15,16], i.e., by movement of the cells under the influence of a non-uniform, alternating electric field of low intensity. This results in the formation of so-called pearl chains, the length of which depends on the cell suspension density and the inhomogeneity of the field. (2) Fusion between cells in a pearl chain is induced by an additional external field pulse of short duration and high intensity which results in the reversible electrical breakdown of the cell mem- brane [10,17,18]. Since the dielectrophoretically collected cells are aligned parallel to the field, electrical breakdown predominantly occurs in the contact zone between any two cells. After breakdown, the fusion process takes place within seconds to several minutes, depending on the species. This technique has been successfully applied in the fusion of plant protoplasts of different species, sea urchin eggs and human erythrocytes [6-14]. In the latter case giant fused cells of up to 1 mm diameter were obtained. Here, we report on electric field-induced fusion of a permanent mammalian cell line in order to test the potential of this method for somatic hybridization and for the production of giant cells from mammalian cells which could then be impaled with microelec- trodes. Friend cells (erythroblasts obtained by trans- formation with Friend virus) were used because the biochemical activity and, in turn, viability of the fused cells could easily be determined by means of the dimethylsulfoxide (DMSO)-induced haemogglobin synthesis.
