Membrane microextension: a possible mechanism for establishing molecular contact in electrofusion

True cell membrane contact is an essential condition for electro-pulsed cel l fusion, but initial morphological perturbation leading to true contact is still not clear. Dielectrophoresis mediated compression and fusogenic puls e induced compaction of cells led to rapid merger of tight membranes, and d eprived direct microscopic view of surface membrane perturbation. Freely su spending cells with large and different cell-cell gaps may proceed to elect rofusion with perturbed membrane and initiates fusion events at different t ime. These pulsed exposed cells can be used for capturing changes in the me mbrane surface and early electrofusion events. Early stage of fusion of fre ely suspended intact human erythrocytes exposed to single exponential decay pulse was studied by scanning electron microscopy (SEM). Field pulse induc es small membrane bumps. Interaction of bumps on adjacent membranes lead to true membrane contact and form bridges between the membranes as microexten sion, combining both membranes into a topologically single structure. Some fusion products showed expanded fusion zones, which suggest indication of o pen lumen at contact area. (C) 1999 Elsevier Science S.A. All rights reserv ed.