Physiological levels of diacylglycerols in phospholipid membranes induce membrane fusion and stabilize inverted phases

In a previous paper, it was shown that liposome fusion rates are substantially enhanced under the same conditions which induce isotropic 31P NMR resonances in multilamellar dispersions of the same lipid. Both of these phenomena occur within the same temperature interval, ΔTI, below the Lα/HII phase transition temperature, TH. TH and ΔTI can be extremely sensitive to the lipid composition. The present work shows that 2 mol % of diacylglycerols like those produced by the phosphatidylinositol cycle in vivo can lower TH, ΔTI, and the temperature for fast membrane fusion by 15-20 degree C. N-Monomethylated dioleoylphosphatidylethanolamine is used as a model system. These results show that physiological levels of diacylglycerols can substantially increase the susceptibility of phospholipid membranes to fusion. This suggests that, in addition to their role in protein kinase C activation, diacylglycerols could play a more direct role in the fusion event during stimulus-exocytosis coupling in vivo