FREQUENT FUSION OF LIPOSOMES TO A POSITIVELY CHARGED PLANAR BILAYER WITHOUT CALCIUM-IONS

A novel positively charged planar bilayer membrane was formed from a m ixture containing 20% cationic lipid, 1,2-dioleoyloxy-3-(trimethylammo nio)propane, and neutral phospholipid mixture of 56% phosphatidylethan olamine and 24% egg phosphatidylcholine. The basic properties of the b ilayer were essentially the same as those previously reported for neut ral and negatively charged lipid bilayers. Using the positively charge d bilayer in addition to neutral and negatively charged bilayers, the effects of charge of the planar bilayers upon vesicle-planar membrane fusion were investigated by measuring the fusion, to the bilayers, of liposomes containing nystatin-ergosterol channels and carrying a net n egative charge. The tendency for fusion was evaluated in terms of the time elapsed before the first fusion event (denoted fusion time). In t he absence of calcium ions, a fusion time of about 1 min was measured with the positively charged planar bilayers, and about 5 and over 15 m in with the neutral and negatively charged planar bilayers, respective ly. These results indicated that the vesicle-planar membrane fusion wi thout calcium ions is greatly enhanced by the presence of cationic lip ids in the planar bilayers, and suggested the usefulness of cationic l ipid bilayers.