Permeability and Conductance of Ion Channels A Primer

Abstract

The purpose of this chapter is to provide an introduction to conductance and permeability, the two phenomenological parameters that are universally used to describe the process of ion permeation through channels. Both of these parameters contain information about how easy or difficult it is for an ion to enter a channel, move through it, and exit on the other side, but in some cases conductance and permeability can report different aspects of the permeation process. This difference arises because it is possible to use the term permeability in two different ways. Permeability can be used as a measure of how readily an ion will cross a membrane via an open channel. I will refer to this as the apparent permeability because it is a reflection of the nature of the interaction of a particular test ion with the channel, but can also include a contribution due to competition from other ions that can limit accessibility of the channel to the test ion. It is possible in principle, however, to circumvent these latter effects experimentally, and determine what I shall call the intrinsic permeability, that is, a measure of the interaction of the test ion with the channel in the absence of competition from other ions.