Fusion of negatively charged phospholipid vesicles by alpha-latrotoxin.

alpha-Latrotoxin-induced fusion of liposomes has been described using large unilamellar vesicles composed of phosphatidylcholine/phosphatidylethanolamine/cardiolipin at a molar ratio of 2:3:5. Vesicle fusion was monitored by terbium/dipicolinic acid assay as well as by fluorescence energy transfer measurement. The enhancement of the fusogenic effect of LTX by low concentrations (0.1-3 mM) of CaCl2 has been demonstrated. The efficiency of other divalent cations on the LTX fusogenic activity was shown to decrease in the sequence Ca greater than Cd greater than Sr greater than Mg greater than Ba. LTX-induced fusion was accompanied by the increase of vesicle size measured by laser correlation spectroscopy. It is concluded that fusogenic action of LTX may be involved in its effect on synaptic apparatus.