The issue of membrane capacitance (C) is re-examined. The influence of fluctuations is studied using the non-local electroelastic model developed previously. The effect of undulations is compared with that due to voltage-induced thinning of the bilayer. It is shown that the undulatory contribution to the voltage dependence of C is significant at small surface tensions, but at higher tensions the role of compression becomes dominant. At all tensions, the effect of non-locality does not exceed 15–20% of the total undulatory contribution. The same results hold if ionic screening by the electrolyte (in a Poisson-Boltzmann approximation) is taken into consideration.

Handbook of Biological Physics

Membrane capacitance: a non-local electroelastic treatment

A micropipette suction method was adapted for the characterization of cell adhesion to polymer surfaces. The instrument was applied in experiments probing the adhesion of human erythrocytes to polymer films which had been precoated with monoclonal antibodies against two different transmembrane proteins of the cells. Cells were impinged on the polymer substrates and subsequently removed by stepwise micropipette aspiration. Variations of shape and contact area of the cells during micropipette aspiration-driven detachment were evaluated to determine the separation energy. A strong increase of the separation energy with decreased contact area was observed and explained by the smoothing of the cell membrane at elevated membrane tensions. The results indicate that the overall strength of attachment was determined by the amount and availability of the adsorbed antibodies, while the separation of the cells from the polymer substrates occurred, in general, due to dislocation of the transmembrane proteins from the ...

Cell adhesion to polymer substrates characterized by the micropipette aspiration technique

The nucleus of the eukaryotic cell contains a large pool of lipids together with structural proteins and genomic DNA. The project aim was to develop simple and robust lipid and DNA models that will allow for these complex molecules to be mixed together in order to elucidate the possible interactions. The large percentage of lipids found within the nucleus makes it likely that they exist in aggregates, although the actual role and structure in which they exist is unknown. While there has not been substantial work done to model such interactions between lipids and DNA in order to better understand the interactions within the nucleus, a substantial body of work exists on lipid/DNA complexes in relation to gene therapy. These simulations in many cases however, are too simple and the structures formed are pre-imposed to a certain degree. Our model would attempt to simulate these interactions without such pre-imposed conditions relying solely on interactions between the particles to drive the structures being formed. A coarse graining approach in which several groups of atoms are subsumed into single interaction sites was deemed suitable given the complexity of modelling a mixture of DNA and lipids, together with the solvent and ion environment. In this regard new models of lipids, DNA, ion and solvent models were developed in a purpose built molecular dynamics package called LANKA-Lipid And Nucleic acid Komputer Algorithm. The lipids in the model are represented as polar ellipsoids and the solvent as spheres with dipoles embedded within them. The interactions between the lipids and solvent are modelled using the Gay Berne potential. The developed lipid model was able to self assemble into a stable bilayer phase and reproduce many bilayer properties of a liquid crystal phase. The model was then extended to capture some of the other lipid phases seen in nature, including lyotropic phase transitions. A simple study of lipid mixtures has also been undertaken during this period. The importance of considering multicomponent lipid systems has increasingly been highlighted in the literature to make the lipid models more realistic. The developed lipid models are simple enough to extend and attempt to simulate the formation of lipid rafts and domain formation. Simulation of DNA in the past has largely focused on atomistic studies. While these have proved valuable they do not consider the macroscopic length scales of the molecule. Simplified models trying to capture long length scales have had to compromise on the molecular level detail. Coarse grain models while trying to bridge the gap have also remained largely idealistic in nature.

Handbook of Biological Physics

Citations

Membrane capacitance: a non-local electroelastic treatment

Cell adhesion to polymer substrates characterized by the micropipette aspiration technique

Computer simulation of lipids and DNA using a coarse grain methodology

Simulation and modeling of polyelectrolyte gels

Cytoskeletal organization in biomimetic liposomes

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