Mitochondrial membranes with mono- and divalent salt: Changes induced by salt ions on structure and dynamics

We employ atomistic simulations to consider how mono- (NaCl) and divalent (CaCl2) salt affects properties of inner and outer membranes of mitochondria. We find that the influence of salt on structural properties is rather minute, only weakly affecting lipid packing, conformational ordering, and membrane electrostatic potential. The changes induced by salt are more prominent in dynamical properties related to ion binding and formation of ion-lipid complexes and lipid aggregates, as rotational diffusion of lipids is slowed down by ions, especially in the case of CaCl2. In the same spirit, lateral diffusion of lipids is slowed down rather considerably for increasing concentration of CaCl2. Both findings for dynamic properties can be traced to the binding of ions with lipid head groups and the related changes in interaction patterns in the headgroup region, where the binding of Na+ and Ca2+ ions is clearly different. The role of cardiolipins in these phenomena turns out to be important.