Interactions of water‐soluble fusogens with phospholipids in monolayers

In earlier work it was proposed that unsaturated fatty acids and their derivatives may induce erythrocytes to fuse by increasing the proportion of hydrocarbon chains in the membrane that are in a relatively liquid state [ 1,2] . From a spectrofluorimetric study, it has been suggested that the action on erythrocyte ghosts of the fusogenic lipid, glycerol mono-oleate, is also at least partially a fluidizing one [3], and from investigations using the ‘membrane mobility agent A2C’ it has been concluded that it seems reasonable to suppose that some increase in local fluidity in membranes favours cell fusion [4]. Similarly, the fusion of phospholipid vesicles with one another in model systems requires the lipids of the interacting membranes to be in a fluid state [5]. Bij contrast dimethyl sulphoxide, which enhances the rate of fusion of acidic phospholipid vesicles [6], as well as inducing cell fusion [7], has been found to produce an increase in the transition temperature of acidic dimyristoylphosphatidylglycerol membranes [8]. It was therefore proposed that membrane fusion induced by dimethyl sulphoxide may, like the action of Ca’+, involve isothermal phase transitions in the lipids of membranes [9]. We have previously reported that water-soluble fusogens interact with and markedly decrease the surface potential of monolayers of phosphatidyl-