The permeability of liposomes to nonelectrolytes. II. The effect of nystatin and gramicidin A.

The process of selective permeation of nonelectrolytes across liposomes of different lipid composition and amount of cholesterol has been studied. The extent of the selectivity for diffusion within the membranes has been found to be related to the physical state of the hydrocarbon chains. It has been also found that incorporation of cholesterol into egg-lecithin membranes decreases the overall permeability by affecting the dehydration step more than the subsequent diffusion of the solute. The incorpporation into liposomes of the antibiotics nystatin and gramicidin A produces changes in the selective permeation of nonelectrolytes that are consistent with the formation by these molecules of aqueous pores of fixed dimensions. Finally, comparisons are made between the process of permeation in biological membranes and in liposomes with and without antibiotics.