Answers to two questions asked at the end of my talk:

1)  Why is there an electric field across the membrane?

Answer:
The cell needs to rid itself of enough ions so as to reduce its osmolarity (its tendency to absorb water (and so to burst)); it does this by pumping out 3 Na⁺  while bringing in 2 K⁺.   The cell assumes a net negative charge, resulting in an inward electric field across the membrane of about 15 million Volts per meter.  The potential drop is 60 mV across the 4 nm membrane.  So the field is due to the cell's efforts not to burst.

2)  How can a polycation cross a membrane?  Why does one with nine R's enter more easily than a single R?

Answer:
The force pulling the polycation across a membrane is qE while the opposing force is felt only as each cation crosses from saline to lipid, and so is independent of the number of cations.  Also, if the polycation is long enough, the first few cations help pull the polycation across a membrane as they cross from lipid to the cytosol.