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Witold Subczynski, Marija Raguz, Laxman Mainali, William J O'Brien; Lateral Organization of Lipids in Plasma Membranes of Fiber Cells Isolated from Single Donor Human Eye Lenses. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5724.
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© ARVO (1962-2015); The Authors (2016-present)
Human lenses may differ not only because of age, but also because of the varying health history of the donor. The purpose of these studies was to obtain detailed information about lateral organization and properties of the lipid bilayer portion of fiber cell membranes isolated from two lenses from a single donor. Results were compared taking into account the age of donor and, if available, donor’s health history.
Intact fiber cell membranes from cortical and nuclear regions of two lenses obtained from single donors were isolated separately and investigated using EPR spin-labeling methods. Phospholipid analogs (n-SASLs) and cholesterol analog (ASL) were used to locate the nitroxide moiety of a spin label at different depths and in different domains in the lipid bilayer portion of intact fiber cell plasma membranes. These approaches allowed us to obtained detailed profiles of the phospholipid alkyl chain order, alkyl chain fluidity, oxygen transport parameter, and hydrophobicity across membrane domains. They also allowed the quantification of lipid domains in intact membranes.
Intact membranes from eyes of all donors were found to contain three distinct lipid environments termed the bulk lipid domain, boundary lipid domain, and trapped lipid domain. However, the cholesterol bilayer domain, which was detected in cortical and nuclear lens lipid membranes, was not detected in intact membranes. The amount of lipids (phospholipids and cholesterol) in domains uniquely formed due to the presence of membrane proteins (boundary and trapped lipid domains) was greater in nuclear membranes than in cortical membranes. Additionally, the amount of lipids in these domains, both in cortical and nuclear membranes, increased with the age of the donor. The lipid-bilayer portions of intact membranes affected by membrane proteins (boundary and trapped lipids) were significantly less fluid than the lipid bilayer which is not affected by the presence of integral membrane proteins (bulk lipids).
All of these new methods, which allow for the quantification of lipid domains in intact fiber cell membranes, combined with the measurements of samples from a single donor, have the potential to be a powerful approach for studying changes in fiber cell membranes occurring with age and with cataract formation.
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