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Marija Raguz, Laxman Mainali, William J. O'Brien, Witold K. Subczynski; Characterization of Intact Fiber-Cell Plasma Membranes Isolated from Cortical and Nuclear Regions of Human Eye Lenses from Different Age Groups. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3028.
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© ARVO (1962-2015); The Authors (2016-present)
We hypothesize that aging affects structure and dynamics of the lipid-bilayer portion of the fiber-cell membrane as well as formation of different lipid domains within the membrane.
The physical properties of intact fiber-cell membranes isolated from human lenses, including profiles of the alkyl chain order, hydrophobicity, and oxygen transport parameter were investigated using conventional and saturation-recovery electron paramagnetic resonance (EPR) spectroscopy and lipid spin labels. These methods provide unique opportunity to discriminate coexisting lipid domains.
The physical properties, obtained for cortical and nuclear membranes isolated from pools of 20 human lenses for four age groups (0-20, 21-40, 41-60 and 61-80 year old) were compared. All investigated membranes were found to contain three distinct lipid environments: bulk, boundary, and trapped lipid domains. The amount of boundary and trapped lipids was greater in membranes from nuclear than from the cortical region. It was difficult to detect pure cholesterol bilayer domains (CBDs) in membranes from the nuclear region because the oxygen transport parameter measured in the CBD was the same as in the domain formed by trapped lipids (lipids in protein aggregates). It was evident that the rigidity of nuclear membranes was greater than that of cortical membranes for all age groups. The permeability coefficient for oxygen across the bulk-boundary domain of cortical membranes was ~50% higher than that across the nuclear membrane. The same parameter across the trapped lipid domain in both membranes was very low and was almost identical for all age goups.
Formation of low oxygen permeability lipid domains was enhanced in membranes of the nuclear region indicating changes in membrane composition. Surprisingly, no significant differences in physical properties of membranes isolated from lenses of different age groups were detected. This was likely a result of pooling together 20 lenses for each age group. Thus, the currently available EPR methodology was able to detect some differences in physical properties of fiber-cell membranes based on the region of the lens from which the membranes were prepared but the parameters that we have measured to date did not disclose age dependent differences.
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