Localization of an entrapped item within unilamellar vesicle compartments: use of ultrasound disruption as a procedure to separate aqueous phase and lipidic lamellae.

A procedure has been carried out previously to separate the aqueous phase and the lipidic lamellae from multilamellar liposomes (Bakouche and Gerlier, Analyt. Biochem., 1983, 130, 379). This procedure consisted in multiple short bursts of sonication at a temperature below the transition temperature (Tm) of the lowest melting component followed by an ultracentrifugation. The aqueous phase and the lipidic lamellae were recovered in the supernatant and in the pellet respectively. This procedure was adapted for unilamellar vesicles by modifying the second step of the procedure. A suspension of unilamellar liposomes containing 5,6-carboxyfluorescein (5,6-CF) as a probe for the aqueous phase was disrupted by sonication at low temperature. After gel filtration on to a Sephadex G100 column, the phospholipid bilayers were readily separated from the aqueous probe 5,6-CF. Such a procedure should allow the localization of any item within the unilamellar liposome compartments.