Single-length and double-length channels formed by nystatin in lipid bilayer membranes

Nystatin forms two types of channels in sterol-containing planar bilayer membranes. One type is formed when it is added to only one side of the membrane: the other is formed when it is added to both sides of the membrane. The relative permeability of these channels to nonelectrolytes (urea and glycerol) is identical. The sensitivity of membranes to the one-sided action of nystatin is critically dependent on their thickness; in particular, membranes made from monoglycerides with more than 18 carbon atoms in their acyl chain are insensitive to nystatin's one-sided action. These data are consistent with a model in which the two types of channels formed by nystatin have essentially identical structures, except that the channel formed by its two-sided action is twice the length of that formed by its one-sided action, because it is a tail-to-tail dimer of the latter.