Photoinduced fusion of liposomes.

Abstract

The photopolymerization of two-component large unilamellar liposomes (LUV) composed of 3/1 dioleoylphosphatidylethanolamine (DOPE) and either 1,2-bis- (10-(2',4'-hexadienoyloxy)decanoyl) -sn-glycero-3-phosphatidylcholine (bis-SorbPC) or 1-palmitoyl-2- (10-(2$\sp\prime,4\sp\prime$-hexadienoyloxy) decanoyl) -sn-glycero-3-phosphocholine (mono-SorbPC) facilitated liposome fusion. Fusion was characterized by fluorescent assays for lipid mixing, aqueous contents mixing, and aqueous contents leakage. The rate and extent of the photoinduced fusion was dependent on the extent of polymerization, temperature, and the fusion initiation conditions, including the pH and the presence of Mg²⁺ ions. Examination of the temperature dependence of fusion for unpolymerized and polymerized liposomes showed that an enhancement of the rate of fusion occurred in the temperature range, Δ T(I), where inverted phase lipid intermediates are observed. Photopolymerization causes lateral separation of the liposome components and thereby results in the isothermal induction of fusion by lowering the threshold temperature for formation of fusion intermediates.