Liposome fusion, fluorescence microscopy

One facile method for investigation of cellular interactions of liposomes, and more precisely, their ability to accumulate within cells, is the fluorescent microscopy. To meet this objective, liposomes are loaded with fluorescent marker (calcein or other suitable dye) at high concentration, whereby its fluorescence is self-quenched. Upon cellular fusion and internalization the dye is released from the carrier, diluted in the environment so the selfquenching effect is lost and the increased fluorescence is detected by fluorescent microscopy. In the case of effective cellular internalization of pH-sensitive liposomes, that is, without endosomal sequestration, calcein would have been diluted several-hundred-fold and the cells will display uniform cytosolic fluorescence. If the liposomes have been taken up by cells by endocytosis, punctuate fluorescence will be restricted to the secondary lysosomal and endocytic vacuoles. In contrast, adsorbed liposomes should... 

Fluorescence Microscopy of Liposome Fusion onto a DOPC-coated Hg Interface... 

Jelinek and co-workers demonstrated that the changes in fluorescence of PDA can be used to detect the interactions of drug molecules with the membranes of live cells. Diacetylene patches containing 10,12-tricosadiynoic acid were transferred from diacetylene vesicles to the membranes of leukemia cells and were polymerized with UV radiation. This fusion efficiency was found to depend on the lipid composition of the liposomes and the presence of cholesterol on the plasma membrane. The interactions of these cells with lidocaine (a local anesthetic), polymixin-B (an antibiotic), and oleic acid were studied by confocal fluorescence microscopy. The PDA patch on the live cells showed bright red fluorescence when the cell membranes were perturbed. The blue to red color change in the presence of oleic acid was apparent when the cells were sedimented by centrifugation. 

Modification of Cells for Transport Experiments Experimental control of intracellular environment, 171, 817 implantation of isolated carriers and receptors into living cells by Sendai virus envelope-mediated fusion, 171, 829 resonance energy transfer microscopy visual colocalization of fluorescent lipid probes in liposomes, 171, 850. 

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