Influence of torus on the capacitance of asymmetrical phospholipid bilayers.
We have measured the specific capacitance of phosphatidylethanolamine/phosphatidylserine membranes formed from monolayers. The membranes were built across Teflon films whose thickness varied from 6 to 25 mum. The building up of the membranes was followed by recording the capacitance of the membranes during the entire process of their formation. It is observed that the specific capacitance increases by about 10% as the thickness of the film is increased. Furthermore, during formation of the membrane it is observed that the capacitance values increased markedly immediately before the membranes are completely formed and then suddenly decrease to their normal values when formed (closing-off phenomenon). These results have led us to propose that the transition region known to surround membranes formed from monolayers may affect the capacitance values measured for such membranes. However, this effect is indirect in the sense that the composition (most likely in the form of inverted micelles) of the transition region will ultimately modify the hydrophobic/hydrophilic barrier in the bilayer by affecting the lateral tension known to exist in such membranes and, as a consequence, the average molecular area occupied by a phospholipid molecule in the bilayer. By such a mechanism, one can rationalize our experimental finding that the membrane capacitance varies as a function of the partition thickness across which they are prepared. It also rationalizes the large fluctuations in capacitance values usually found in the literature for such membranes as well as, at least in part, the closing-off phenomenon.
Brullemans
M
M
University of Quebec, Photobiophysics Research Center, P.O. Box 500, Trois-Rivières, Québec G9A 5H7, Canada.
Tancrde
P
P