1: Biophys J  1993 Jun;64(6):1789-800 

Time courses of cell electroporation as revealed by submicrosecond imaging of
transmembrane potential.

Hibino M, Itoh H, Kinosita K Jr.

Department of Physics, Faculty of Science and Technology, Keio University,
Kanagawa, Japan.

Changes in the membrane conductance of sea urchin eggs, during the course of
electroporation, were investigated over the time range of 0.5 microsecond to 1
ms by imaging the transmembrane potential at a submicrosecond resolution with
the voltage-sensitive fluorescent dye RH292. When a rectangular electric pulse
of moderate intensity was applied across an egg, a position-dependent potential
developed synchronously with the pulse, as theory predicts for a cell with an
insulating membrane. From the rise and fall times, the membrane capacitance of
unfertilized eggs was estimated to be 0.95 microF/cm2 and the intracellular
conductance 220 omega.cm. Under an electric pulse of much higher intensity, the
rise of the induced potential stopped at a certain level and then slowly
decreased on the microsecond time scale. This saturation and subsequent reversal
of the potential development was ascribed to the introduction of finite membrane
conductance, or permeabilization of the membrane, by the action of the intense
pulse (electroporation). Detailed analysis indicated the following: already at
0.5 microsecond in the rectangular electric pulse, the two sides of the egg
facing the positive and negative electrodes were porated and gave a high
membrane conductance in the order of 1 S/cm2; the conductance on the positive
side appeared higher. Thereafter, the conductance increased steadily, reaching
the order of 10 S/cm2 by 1 ms. This increase was faster on the
negative-electrode side; by 1 ms the conductance on the negative side was more
than twice that on the positive side. The recovery of the porated membrane after
the pulse treatment was assessed from the membrane conductance estimated in a
second electric pulse of a small amplitude. At least two recovery processes were
distinguished, one with a time constant of 7 microseconds and the other 0.5 ms,
at the end of which the membrane conductance was already < 0.1 S/cm2.

PMID: 8369408 [PubMed - indexed for MEDLINE]