Carrier-like behaviour from a static but electrically responsive model pore.

Because of the low dielectric constant of most proteins and lipids, the electric field of an ion passing through a narrow pore is long range and will interact with neighbouring ionizable residues of the channel protein. The electrical structure of the channel may thus change transiently in response to an ion passing through the pore. Model calculations then reveal that the ratio of the unidirectional ion fluxes may approach 1 as expected for a carrier or shuttling ionophore rather than the Ussing ratio expected for a pore. Saturation behaviour also becomes carrier-like. Computer simulation is reported showing a continuous variation between pore-like and carrier-like behaviour as the parameters of the system are allowed to change smoothly.