Turbidity changes of lipid vesicles near the phase transition temperature as an indication of fusion.

Sonicated liposomes of dipalmitoyl phosphatidylcholine show sharp turbidity changes on heating at two distinct temperatures. A decrease in turbidity at the lower temperature (approx. 37degrees C) is thought to be associated with the phase transition of small vesicles and a decrease at about 44 degrees C with larger vesicles or multilayer. An increase of turbidity between 38 and 43 degrees C is attributed to the fusion of small vesicles. The turbidity changes were studied under various modes of vesicle preparation to confirm the interpretation of the turbidity data. Alternate interpretations are discussed.