Abstract
The mechanism of ion channel formation in bilayer lipid membranes is discussed by comparing the experimental behavior of current-time and current-voltage curves with the predictions of a model accounting for the kinetics of nucleation of monomeric units and growth of the resulting channel-forming aggregates. A distinction is made between channel-forming peptides, whose dipoles are oriented normal to the membrane plane by the electric field, and large proteins aggregating into Na+, K+, and Ca2+ channels, which have a constant transmembrane disposition and merely reorient each other with a parallel side-by-side motion under the influence of the electric field. This difference explains why the open probability, as expressed in both cases by the one-sided Boltzmann equation, attains the unit value at accessible depolarizations in protein ion channels, whereas it is much less than unity in peptide ion channels.
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