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Abstract
Cells can be transiently permeabilized by exposing them briefly to an intense electric
field (a process called "electroporation"), but it is not clear what structural changes
the electric field induces in the cell membrane. To determine whether membrane pores
are actually created in the electropermeabilized cells, rapid-freezing electron microscopy
was used to examine human red blood cells which were exposed to a radio-frequency
electric field. Volcano-shaped membrane openings appeared in the freeze-fracture faces
of electropermeabilized cell membranes at intervals as short as 3 ms after the electrical
pulse. We suggest that these openings represent the membrane pathways which allow
entry of macromolecules (such as DNA) during electroporation. The pore structures
rapidly expand to 20-120 nm in diameter during the first 20 ms of electroporation,
and after several seconds begin to shrink and reseal. The distribution of pore sizes
and pore dynamics suggests that interactions between the membrane and the submembrane
cytoskeleton may have an important role in the formation and resealing of pores.