Surface behavior of axolemma monolayers: Physico‐chemical characterization and use as supported planar membranes for cultured Schwann cells

Abstract

The axolemma membrane forms a stable and reproducible monomolecular layer at the air-aqueous interface. The major lipids and proteins are present in this monolayer in molar ratios similar to the original membrane. Acetylcholinesterase and Na-K-ATPase activities are preserved in the monolayer to levels of 64% and 25%, respectively. The total lipid fraction forms a homogeneously mixed phase. The presence of proteins in the monolayer introduces surface inhomogeneties. Among other features, this is revealed by the presence of two values of lateral pressure at which the monolayer shows partial or total collapse: a broad partial collapse at surface pressures between 13 to 30 mN/m and a sharp collapse point at 46 mN/m. The average molecular areas, the broad collapse point, and the variation of the surface potential per molecule suggest the relocation of protein components at surface pressures between 13 to 30 mN/m. The behavior is consistent with the extrusion and exposure of proteins toward the aqueous medium that depends on the lateral pressure. Schwann cells grown on coverslips coated with axolemma monolayers at 13 mN/m (beginning of the broad collapse) and 34 mN/m (above the broad collapse) recognize the difference in the surface organization of axolemma caused by the lateral pressure which affects their proliferation, morphology, and spatial pattern of organization. Our results show for the first time that response of Schwann cells depends on the intermolecular organization of the axolemma surface with which they interact. These results suggest that the local expression of putative surface molecules of axolemma that may mediate membrane recognition and the signalling of morphological and proliferative changes can be modulated by long range supramolecular properties.

Sphingomyelinase acts by an area-activated mechanism on the liquid-expanded phase of sphingomyelin monolayers

“…Monolayers were transferred from the airwater interface to solid supports. To perform the transference, the coverslip was held above the monolayer and slowly lowered until touching it (23). After a few seconds, the coverslip was pushed through the monolayer.…”

Langmuir Films from Human Placental Membranes: Preparation, Rheology, Transfer to Alkylated Glasses, and Sigmoidal Kinetics of Alkaline Phosphatase in the Resultant Langmuir-Blodgett Film

“…Once formed, films were particularly stable and could be manipulated without any detectable loss. This procedure was used to characterize lipoprotein films derived from intestinal brush border membranes [21,22], human erythrocyte and Escherichia coli (cytoplasmic) membranes [22,23], rabbit sarcoplasmic membranes [23], myelin [24], and axolemma [25]. Moreover, the monolayer can be transferred to an alkylated glass to obtain a planar supported, Langmuir-Blodgett (LB), film conserving the molecular organization of the original floating monolayer [20,26,27].…”

Composition-driven Surface Domain Structuring Mediated by Sphingolipids and Membrane-active Proteins

“…Such solubility is quite unique for myelin and, in fact, it constitutes a purity criterion [285]; this represents a clear advantage for quantitative monolayer spreading at the air/water interface because surface pressure-molecular area compression isotherms can be directly calculated from the spread amount of myelin [286]. More generally, biomembrane monolayers can also be spread from aqueous suspension [165,[279][280][281][282]286] by applying the method of Trurnit [287], commonly used for the spreading of hydrophilic polymers and proteins, but this approach is rather laborious because the tiny amounts of material at the interface must be collected and quantified for determining surface pressure-mean molecular area isotherms. The adsorption of interfacial (Gibbs) films from myelin vesicles from the subphase [288] opened the possibility of working with these mono-or multi-layered interfaces [286,289].…”

“…However, attempts to form compositionally complex monolayers with whole natural membranes, while deriving some meaningful molecular information, were absent for years [280][281][282].…”