  The electropermeabilization of biological cell membranes by the application
of an external field occurs whenever an applied field exceeds a threshold
value. For fields above this threshold value but less than another critical
value, the pores formed in the membrane are transient or reversible. Several
mechanisms have been proposed for the formation of these transient pores. Here
we examine the local electric fields generated for the configuration of cells
embedded in a polycarbonate filter, both in the region in and around the pore.
We consider the shear forces created in the membrane due to the gradient of the
field along the surface of the membrane, and the interaction of the charged
molecules in the membrane with this field. A relationship between the electric
field strength and the size of the pore formed is derived.
