1: Biophys J  1996 Dec;71(6):3242-50 

Preparation of giant liposomes in physiological conditions and their
characterization under an optical microscope.

Akashi K, Miyata H, Itoh H, Kinosita K Jr.

Department of Physics, Faculty of Science and Technology, Keio University,
Yokohama, Japan.

Unilamellar liposomes with diameters of 25-100 microns were prepared in various
physiological salt solutions, e.g., 100 mM KCl plus 1 mM CaCl2. Successful
preparation of the giant liposomes at high ionic strengths required the
inclusion of 10-20% of a charged lipid, such as phosphatidylglycerol,
phosphatidylserine, phosphatidic acid, or cardiolipin, in phosphatidylcholine or
phosphatidylethanolamine. Three criteria were employed to identify unilamellar
liposomes, yielding consistent results. Under a phase-contrast microscope those
liposomes that showed the thinnest contour and had a vigorously undulating
membrane were judged unilamellar. When liposomes were stained with the
lipophilic fluorescent dye octadecyl rhodamine B, fluorescence intensities of
the membrane of individual liposomes were integer multiples (up to four) of the
lowest ones, the least fluorescent liposomes being those also judged unilamellar
in the phase-contrast image. Micropipette aspiration test showed that the
liposomes judged unilamellar in phase and fluorescence images had an area
elastic modulus of approximately 160 dyn/cm, in agreement with literature
values. The giant liposomes were stable and retained a concentration gradient of
K+ across the membrane, as evidenced in fluorescence images of the
K(+)-indicator PBFI encapsulated in the liposomes. Ionophore-induced K+
transport and associated volume change were observed in individual liposomes.

PMID: 8968594 [PubMed - indexed for MEDLINE]