STRUCTURAL STUDIES ON PHOSPHOLIPID BILAYERS

M. Suwalsky*, F. Villena, B. Ungerer and C.P. Sotomayor

*Faculty of Chemical Sciences, University of Concepcion, Casilla 3-C, ConcepciBn, Chile

'Phospholipids are large natural amphipathic molecules that have long hydrophobic hydrocarbon chains, saturated and/or unsaturated, and polar zwitterionic polar headgroups. In contact with water phospholipids spontaneously assemble into higher molecular aggregates. However, the most relevant phase is the bilayer for its relation to the structure, properties and functions of cell membranes. These are very complex entities. They are not only constituted by an extremely large number of different molecules but they show a very low degree of periodical order. This has led to the proposal of several different models of which that of Singer and Nicolson has been widely accepted. Therefore, given the complexity of cell membranes, simpler models based on phospholipid bilayers are widely used.

We have determined the structure of lecithin and cephaline multilayers. These are types of phospholipids that are respectively located in the outer and inner monolayers of most biomembranes. Besides, we have studied the perturbing effect of water upon their structures. Since then, we have been using lecithin and cephalin bilayers as models to study the way different chemicals interact with cell membranes. This is achieved by making them to interact under a wide range of concentrations in hydrophobic and aqueous media at a constant temperature. The structure perturbation induced to the phospholipid bilayers is followed by X-ray techniques. The results we have obtained in these models have allowed us to interpret the effects these compounds have produced to cell membranes, both in vivo and in vitro. In fact, human erythrocytes, myelin from rat sciatic nerve and neuroskin tissue from toad have been respectively studied by scanning electron microscopy, X-ray fiber diffraction and electrophysiological measurements. It has been found a good correlation between the results observed in the models and the biological systems. The compounds we have analyzed so far are mainly antibiotics, tranquilizers, antiarrhythmic drugs, pesticides and metallic ions.

~FONDECYT (1930504) and DIUC (95.24.04-1) grants are acknowledged.