  We consider DNA-cationic lipid complexes that form lamellar stacks of lipid
bilayers with parallel DNA strands intercalated in between. We calculate the
electrostatically induced elastic deformations of the lipid bilayers. It is
found that the membranes undulate with a periodicity that is set by the DNA
interaxial distance. As a consequence the lamellar repeat distance changes
resulting in a swelling or compression of the lamellar stack. Such undulations
may be responsible for the intermembrane coupling between DNA strands in
different layers as it is observed experimentally.
