A simple electrical model for biological cells predicts an increasing proba
bility for electric field interactions with cell substructures of prokaryot
ic and eukaryotic cells when the electric pulse duration is reduced into th
e sub-microsecond range. The validity of this hypothesis was verified exper
imentally by applying electrical pulses with electric field intensities of
up to 5.3 MV/m to human eosinophils in vitro. When 3-5 pulses of 60 ns dura
tion were applied to human eosinophils, intracellular granules were modifie
d without permanent disruption of the plasma membrane. In spite of the extr
eme electrical power levels applied to the cells thermal effects could be n
eglected because of the ultrashort pulse duration. The intracellular effect
extends conventional electroporation to cellular substructures and opens t
he potential for new applications in apoptosis induction, gene delivery to
the nucleus, or altered cell functions, depending on the electrical pulse c
onditions. Bioelectromagnetics 22:440-448, 2001. (C) 2001 Wiley-Liss. Inc.