Comparison of two liposome fusion assays monitoring the intermixing of aqueous contents and of membrane components.
Divalent cation-induced fusion of large unilamellar vesicles (approx. 0.1 micron diameter) made of phosphatidylserine (PS) or phosphatidylglycerol (PG) has been studied. Intermixing of aqueous contents during fusion was followed by the Tb/dipicolinic acid fluorescence assay, and intermixing of membrane components by resonance energy transfer between fluorescent lipid probes. Both assays gave identical threshold concentrations for Ca2+, which were 2 mM for PS and 15 mM for PG. The dependencies of the initial rate of fusion on the concentration of PG vesicles determined by either assay were identical, the order of this dependence being 1.2 in the concentration range of 5-200 microM lipid. For PS liposomes, this order was found to be 1.5 in the fluorescent lipid assay. No leakage of contents was detected during the fusion of PG vesicles. Mg2+ inhibited the Ca2+-induced fusion of PS vesicles, but did not cause any fusion by itself, consistent with previous results with the Tb/dipicolinic acid assay.
D000818:Animals; D001921:Brain; D002118:Calcium; D002413:Cations, Divalent; D002417:Cattle; D002459:Cell Fusion; D004735:Energy Transfer; D007700:Kinetics; D008081:Liposomes; D008954:Models, Biological; D010715:Phosphatidylglycerols; D010718:Phosphatidylserines; D013050:Spectrometry, Fluorescence
D002413:Cations, Divalent; D008081:Liposomes; D010715:Phosphatidylglycerols; D010718:Phosphatidylserines; D002118:Calcium