Passage of the Channel-Forming Agent Nystatin Through Ergosterol-Containing Lipid Membranes

The passage of nystatin through the ergosterol-containing phospholipid bilayer was studied on monovesicular and multivesicular giant unilamellar vesicles (GUVs and MVVs). Phase-contrast optical microscopy was used to examine vesicles composed of a palmitoyl-oleoyl-phosphatidyl-choline (POPC) bilayer with either 15 or 45 mol% ergosterol. Three types of vesicles were analyzed: (i) GUVs, (ii) outer vesicles (outGUVs) of MVVs, and (iii) inner vesicles (inGUVs) of MVVs. The times of their ruptures were determined after their exposure to nystatin at concentrations of 250 and 500 $\mu$ M. At both concentrations, the times that the inGUVs spent in the nystatin solution after the rupture of the corresponding outGUVs were significantly shorter than the rupture times of individual GUVs of the similar size. These differences in rupture times demonstrate that the ergosterol-containing POPC membrane is permeable to nystatin.