| Regional Biophysics Meeting 2005, March 16-20, Zreče, Slovenia | [MembBiophys] |
Alkali chlorides play an important role in several biological processes. The specific binding of cations with biological membranes influences not only their fluidity and structure, but consequently also processes like endo- and exocytosis or membrane fusion. Especially calcium ions play a decisive role in neural signal transduction and are believed to be an important driving force of fast transmitter release in the central synapse. In this work we report about the effect of sodium and calcium chloride (0 - 330 mM) on the stability, structure and dynamics of palmitoyloleoylphosphatidylcholine (POPC) bilayers. Combining the techniques of small angle X-ray scattering and spin-label electron paramagnetic resonance spectroscopy, both the global and local parameters of the chosen model membrane systems are characterized. Both salts perturb the positional order within the multibilayer systems considerably. In the case of NaCl we find no significant changes to the overall bilayer structure at all concentrations, but simply a screening of the van der Waals interactions between adjacent bilayers. In contrast, CaCl2 leads at low concentrations to a strong bilayer repulsion, which is completely screened at higher concentrations. In the latter concentration regime we also find a strong increase of the lipid acyl chain order and henceforth an increase of membrane thickness. Our results are confronted with recent molecular dynamics simulation studies, which were carried out on the same model system (see [1] and references therein).
[1] Böckmann, R.A. and H. Grubmüller. 2004. Multistep binding of divalent cations to phospholipid bilayers: a molecular dynamics study. Angew. Chem. Int. Ed. 43: 1021-1024.
Email: michael.rappolt@elettra.trieste.it
Address: DR. MICHAEL RAPPOLT, Institute of Biophysics & X-ray Structure Research, Austrian Academy of Sciences, c/o Sincrotrone Trieste, Strada Statale 14, km 163.5, 34012 Basovizza (Trieste), ITALY.