A new interpretation of flux ratio exponents using statistical rate theory

By viewing permeation as a three-step process (movements between the bulk intracellular medium and the channel, within the channel, and between the channel and the extracellular bulk medium), and describing each step in the process with a statistical rate theory (SRT) approach, we can envisage different permeation scenarios which consider whether movements across certain interfaces can be approximated to be at equilibrium. A new interpretation of the flux ratio exponent is presented and its value can be used to predict whether the rate-limiting region occurs within the channel or at the interface. By considering saturation profiles, estimates for SRT exchange rates can be obtained, and a comparison with the more well-known Eyring rate theory is provided. Received: 27 May 1998 / Revised version: 9 December 1998 / Accepted: 9 December 1998