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M. Raguz, J. Dillon, E. R. Gaillard, W. K. Subczynski; Physical Properties of the Lipid Bilayer Membrane Made of Cortical and Nuclear Cow Lens Lipids: Epr Spin Labeling Studies. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4070. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The lipid composition of fiber cell plasma membranes favors the formation of membrane domains. The current study was conducted to discriminate and characterize purported domains in membranes derived from the total lipids of a two-year-old cow lens cortex and nucleus.
The physical properties of membranes were investigated using EPR spin-labeling methods.
Conventional EPR spectra and saturation-recovery curves show that spin labels detect a single homogenous environment in membranes made from cortex lipids. Properties of these membranes are very similar to those reported by us for membranes made of the total lipid extract of a six-months-old calf lens (J. Widomska, M. Raguz, J. Dillon, E. R. Gaillard, W. K. Subczynski, Biochim. Biophys. Acta 1768 (2007) 1454-1465). However, in membranes made from nucleus lipids, two domains were detected by the discrimination by oxygen transport method using the cholesterol analogue spin label and were assigned to the bulk phospholipid-cholesterol and the pure cholesterol crystalline domains. Because phospholipid analogue spin labels cannot penetrate into the pure cholesterol crystalline domain, they monitor properties of the phospholipid-cholesterol domain outside the pure cholesterol crystalline domain. Profiles of the order parameter, hydrophobicity, and the oxygen transport parameter are practically identical in this domain when measured for either the cortex or nucleus lipids membranes. In both membranes, lipids in the bulk phospholipid-cholesterol domain are strongly immobilized at all depths. Hydrophobicity and oxygen transport parameter profiles have a rectangular shape with an abrupt change between the C9 and C10 positions, which is approximately where the steroid-ring structure of cholesterol reaches into the membrane. The estimated oxygen permeability coefficient across the bulk phospholipid-cholesterol domain in both membranes was only slightly lower than across the water layer of the same thickness as the membrane. However, the evaluated upper limit of the oxygen permeability coefficient across the cholesterol crystalline domain was significantly lower than across the water layer of the same thickness as the cholesterol crystalline domain.
Results indicate that the cholesterol crystalline domain can significantly reduce oxygen transport in the lens nucleus.
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