Properties and Organization of Lipids in Membranes Derived from the Total Lipids Extracted from the Clear Human Lens Cortex and Nucleus of Donors from Different Age Groups

Abstract

Reported results have documented changes that occur with age in the properties and the organization of lens lipid membranes. Results were obtained for membranes derived from the total lipids extracted from the cortex and nucleus of the clear lenses of donors from age groups 0 to 20, 21 to 40, 41 to 60, and 61 to 70 years. The physical properties, including profiles of the alkyl chain order, fluidity, hydrophobicity, and oxygen transport parameter, were investigated using EPR spin-labeling methods, which also provided an opportunity to discriminate coexisting lipid domains and to evaluate the domain's size. All investigated membranes were found to contain two distinct lipid environments: phospholipid-cholesterol domains (PCDs) and pure cholesterol bilayer domains (CBDs). The size of CBDs increased with the donor age and was always greater in nuclear than in cortical membranes. More detailed analysis revealed that the size of CBDs was determined mainly by the cholesterol content in the investigated membranes. Independently of the age-related changes in the phospholipid composition, the physical properties of the PCD remained the same for all age groups and were practically identical for cortical and nuclear membranes. These data additionally confirm that profiles of membrane physical properties do not depend on the phospholipid composition when membranes are saturated with cholesterol.