Ion Dependent Conductance: Switching in Lipid Bilayers

Abstract

THE action of antibiotics on the ionic conductances of lipid bilayers has provided useful models of permeation mechanisms in biological membranes^1,2. Voltage dependent conductance states are of special interest. They have been demonstrated for nerve³ and are probably present, though with much slower kinetics, in other cell types^4,5. There is a distinction between ion selective conductances and ion dependent switching of conductances which themselves may or may not be selective. For example, one has the well known effect of [Ca²⁺] on the Na⁺ conductance⁶ in nerve, and more recently [K⁺] has been shown to increase the inactivation parameter and time constant of this conductance⁷. I wish to describe two examples of the effect of [Na⁺] favouring a low conductance state even though the voltage dependence is opposite in each case and there is no ion selectivity for the conductances.