  Fusion of lipid bilayers in membranes is important in processes from
vesicle-cell interactions (as in drug delivery) to exosome-cell signaling,
while transient transmembrane electric fields are known to occur spontaneously.
Two contacting phosphatidylcholine (PC) lipid membranes are known to fuse into
one under external electric fields, suggesting that the interaction between
them is modified by the field as they approach, prior to the fusion event. Here
we measure directly the adhesion energy between dimyristoylphosphatidylcholine
(DMPC) and between distearoylphosphatidylcholine (DSPC) surface layers attached
to solid substrates both without and with a transmembrane electric field. We
find a marked pressure-dependent adhesion behavior in the electric field, which
we attribute to fusion intermediates that are formed, shedding new light on
membrane electro-fusion.
