Frequent fusion of liposomes to a positively charged planar bilayer without calcium ions.

A novel positively charged planar bilayer membrane was formed from a mixture containing 20% cationic lipid, 1,2-dioleoyloxy-3-(trimethylammonio)propane, and neutral phospholipid mixture of 56% phosphatidylethanolamine and 24% egg phosphatidylcholine. The basic properties of the bilayer were essentially the same as those previously reported for neutral and negatively charged lipid bilayers. Using the positively charged 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 negative charge. The tendency for fusion was evaluated in terms of the time elapsed before the first fusion event (denoted fusion time). In the 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 min with the neutral and negatively charged planar bilayers, respectively. These results indicated that the vesicle-planar membrane fusion without calcium ions is greatly enhanced by the presence of cationic lipids in the planar bilayers, and suggested the usefulness of cationic lipid bilayers.