Triton X-100, sodium dodecylsulphate, sodium cholate, and beta-octylglucoside increase the size of sonicated, but not of unsonicated, phospholipid vesicles above the Tc gel to liquid-crystalline transition temperature. Lysophosphatidylcholine or glyceryl monooleate do not increase liposome size under these circumstances. The observed phenomenon of vesicle growth is virtually unaffected by phospholipid composition, surface potential, calcium ions, EDTA, or albumin. The presence of cholesterol makes the vesicles more susceptible to detergent-induced growth. The presence of detergents, even at concentrations much lower than required to observe any increase in vesicle size, favors the liberation of vesicle contents. These results may have implications concerning membrane fusion as well as the reconstitution of membrane proteins in the presence of detergents.

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Surfactants induce fusion (or increase in size) of sonicated liposomes. This phenomenon is enhanced by cholesterol and inhibited by the intrinsic polypeptide gramicidin A. By comparison with previous physical studies we conclude that liposome ‘fusion’ is facilitated when both fluidity and static order of the bilayer are high.

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