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K. Balantic, V. Weiss, G. Allmaier, D. Miklavcic, P. Kramar:
"Binding effects of calcium ions on different cell membrane models";
Poster: Biophysical Annual Meeting 2021, Boston, MA, USA; 2021-02-22 - 2021-02-26.

Binding effects of metal cations to biological membranes are of considerable interest since ion attachment can alter stability and structure of phospholipid bilayers. Particularly important is the interaction of phospholipids with divalent cations, such as calcium since it plays an important role in a variety of different cellular processes.
The aim of our study was to determine effects of calcium binding to phospholipid membranes employing various cell membrane models, such as planar lipid bilayers and liposomes. What is more, we were able to compare both cell membrane models and gain a better insight on interactions between calcium and phospholipids.
Calcium-binding modifications of phospholipid membranes were determined employing electrical measurements of planar lipid bilayer properties and gas-phase electrophoresis of liposomal particles. Planar lipid bilayers and liposomes were constructed from a mixture of phosphatidylcholine, cholesterol and phosphatidylethanolamine lipids. Planar lipid bilayers were formed using a Muller-Rudin method while liposomes were prepared from dried thin lipid films via hydration.
Changes of phospholipid bilayer thickness due to calcium binding were observed in both of the proposed cell membrane models. A measurable decrease in bilayer resistance and an increase in bilayer capacitance was observed in the presence of calcium ions, which we related to a decrease in planar lipid bilayer thickness as neither changes in bilayer area or electrical constants were reasonable. Furthermore, increased rigidity of the planar lipid bilayers was observed with increasing calcium concentration. Liposome particles decreased in size, which might either be related to tighter packing of phospholipids in the bilayer or local distortions of the lipid bilayer leading to partial loss of encapsulated vesicle components.

cell membrane, liposome, nES GEMMA, gas-phase electrophoresis, calcium