The molecular organization of nerve membranes : V. Properties of mono- and bimolecular films formed with lipids isolated from an axolemma-rich preparation from squid retinal axons.

The formation and properties of mono- and bimolecular films of total lipids extracted from an axolemma-rich preparation from retinal axons of the squid are described.The bilayers formed with α-tocopherol showed resistance values of 10(7) Ω cm(2) indicating their low ionic permeability. These membranes were stable for 30 to 60 min and they behave as an ohmic resistance in the range of -120 to +120 mV.The films formed with these lipids did not discriminate between Na(+) and K(+) and showed a slight selectivity for Cl(-) as compared with cations, indicating a behavior as a rather neutral barrier.The pressure-area characteristics of monolayers built with the phospholipids fraction gave an area of 79 Å(2)/molecule at a pressure of 10 dynes/cm. This expanded molecular area can be accounted for by the unsaturated fatty acid chains of polyenoic structure attached to these phospholipid molecules. The fraction containing 81% cholesterol presented an area of 29 Å(2)/molecule at 10 dynes/cm.Monolayers of the total lipids displayed an area of 51.7 Å(2)/molecule at a pressure of 10 dynes/cm. These findings indicate that the phospholipids, when mixed with cholesterol and free fatty acids, formed rather condensated films. Cholesterol might contribute significantly to increase the cohesive forces in the film and hence to its stability.The expanded films given by the phospholipids extracted from nerve membrane also indicate that they have a low transition temperature; their unusual unsaturated aliphatic chains might be in a special high mobile condition. Their behavior might be important for the position and order of polar groups in an excitable membrane.