Characterization of electric field-induced fusion in erythrocyte ghost membranes.

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Abstract
Fusion was reported to occur in a variety of membrane systems in response to the application of certain electric currents to the medium. The application of a weak but continuous alternating current causes the [human] membranes in suspension to be rearranged into the pearl-chain formation. Fusion can then be induced by 1 or more strong direct current pulses that cause pore formation. This results in the conversion of individual membranes in the pearl-chain formation to a single membrane with 1 or more hourglass constrictions that form lumens which connect the cytoplasmic compartments. As the diameter of the lumens increases, the overall membrane shape grows to 1 large sphere. To further characterize electric field-induced fusion, experiments were conducted using the erythrocyte ghost as a model membrane, and a new combination of electrical circuit and fusion chamber that is simpler and improved over previous systems. All odd-shaped ghosts (collapsed or partly collapsed spherical shapes, echinocytes, discocytes and stomatocytes) in 30 mM phosphate buffer was first converted to spherocytes and then fused with increasing yields by increasing the number of pulses. After fusion, the lateral diffusion of a fluorescent lipid soluble label (Dil) from labeled to unlabeled membranes were observed to occur both with and without the appearance in phase-contrast optics of distinct communication (lumens) between cytoplasmic compartments of the fused membranes. Connections between cytoplasmic compartments were unmistakable with the instant transfer of a fluorescent water-soluble label (fluorescein isothiocyanate-dextran) from labeled to unlabeled cytoplasmic compartments upon fusion. Although pulses still resulted in the lateral diffusion of Dil to unlabeled membranes, the presence of glycerol in the medium strongly reduced the yield of lumens observable by phase-contrast optics in fusion events. The presence of glycerol also inhibited the conversion of membranes to spherocytes, but did not inhibit the lateral diffusion of Dil from labeled to unlabeled membranes.