The Cavity and Internal Pore
Why is there a 10 Å diameter cavity in the
center of the channel with an ion in it
(Fig. 5B and Fig. 6)? Electrostatic calculations
show that when an ion is moved
along a narrow pore through a membrane,
it must cross an energy barrier that is
maximum at the membrane center (17).
The electrostatic field emanating from a
cation polarizes its environment, bringing
the negative ends of dipoles closer to it
and thereby stabilizing it. At the bilayer
center, the polarizability of the surround-