FORMATION OF A MACROSCOPIC MEMBRANE-STRUCTURE BY LIPOSOMES CONTAININGCATIONIC LIPIDS AND EXPOSED TO DC ELECTRIC-FIELDS

Application of DC electric fields (from 20-30.4 kV/m) caused a rapid ( within 1-5 s) formation of a large membrane structure in an aqueous so lution of unilamellar liposomes composed of egg phosphatidylcholine an d a cationic amphiphile, either sphingosine or stearylamine (mole frac tion X = 0.25). The formation of this structure could be readily obser ved by phase contrast microscopy. Maintenance of the membrane required the DC field and it disappeared rapidly (within approximate to 5 s) u pon the removal of the field. The formation of the assembly was revers ible. Such structures were not formed by vesicles composed of phosphat idylcholine only or containing instead of the cationic amphiphile an a nionic lipid, phosphatidic acid. Fusion or a hemifusion of the vesicle s is likely to take place as fluorescence microscopy of liposomes labe led with a pyrene-containing phospholipid analog revealed domain forma tion within the field-induced membrane, evident as a depletion of fluo rescence in the region subjected to highest field intensity. (C) 1997 Elsevier Science Ireland Ltd.