Membrane interaction and deformation.

Membrane interaction and membrane deformation should be considered two aspects of the same phenomenon. Because membrane interaction depends on structural features such as curvature, chemical composition, and surface organization, one must expect that these features will change as membranes are brought together. Our observations on model phospholipid membranes have allowed us to measure and to distinguish electrostatic (coulombic or double-layer) forces, electrodynamic (van der Waals, dispersion) interactions, and hydration forces due to the solvation of polar groups that are stabilizing the membrane surface. As a consequence of these interactions, approaching membranes may flatten against each other, may change the packing density of their constituent molecules, may rearrange the composition of components in regions close to the apposing membrane, or may even show conformational changes in the arrangement of the lipid hydrocarbon chains. Abundant examples of such deformation accompanying membrane interaction are evident from x-ray diffraction and electron microscopic observations.