CONFORMATIONAL MODEL FOR ION PERMEATION IN MEMBRANE CHANNELS - A COMPARISON WITH MULTIION MODELS AND APPLICATIONS TO CALCIUM-CHANNEL PERMEABILITY

The permeation properties of ion channels existing in several conductive states were analyzed. Each state was represented by the one-ion model. A special emphasis was placed on features, assumed to be indicative of a multi-ion mode of channel occupancy such as a deviation of concentration dependence of channel conductance from the Michaelis-Menten equation, an anomalous mole fraction effect, a strong voltage dependence of ion block and coupling of unidirectional fluxes (anomalous Ussing flux ratio). The conformational model was shown to have all these properties. The ion permeation through voltage-sensitive calcium channels fulfilled all the characteristics of the model proposed.