EFFECTS OF MAGNESIUM ON LIQUID AND PHOSPHOLIPIDIC BIMOLECULAR MEMBRANES - MAGNESIUM-ION, A MONOVALENT CATION COMPETITOR

The role of divalent cations, particularly Mg2+, on the structure and properties of artificial membranes of a liquid type (phospholipids dissolved in an organic solvent having low dielectric constant and impregnating a millipore teflon filter) or phospholipid bimolecular membranes was investigated. Resistance and membrane potential were measured using a Keithley 610B electrometer. Mg2+ and other divalent cations act on the structural stability of the membrane. This action is expressed by an increased resistance of membranes having a positive resultant charge (cephalin and lecithin), and a drop in resistance of those having a negative resultant charge (beef brain total lipids). The membrane potential difference is affected, particularly by the total lipids. The effect of Mg2+ is explained by applying the bilayer theory of Gouy and Chapman. Mg2+ has a screening effect; it is absorbed specifically on polar groups of the membrane. This is confirmed by studies which show that Mg2+ is a competitor of monovalent cations in the same membrane site.