Lipid-Protein Interactions in Fiber Cell Plasma Membrane Isolated From Human and Porcine Eye Lenses

Abstract

The protein content in human lens fiber cell plasma membranes is extremely high, increases with age, and is higher in the nucleus than in cortex. This strongly affects the organization and physical properties of the lipid bilayer portion of intact fiber cell plasma membranes including the alkyl chain order, fluidity, hydrophobicity, and oxygen transport parameter. Investigated membranes were isolated from the eye lenses of pigs and human donors. They were studied using electron paramagnetic resonance spin-labeling method that provides an opportunity to discriminate coexisting lipid domains and to evaluate the relative amounts of phospholipids and cholesterol in them. Fiber-cell membranes were found to contain three distinct lipid environments: bulk, boundary and trapped domains that appear due to the presence of membrane proteins. In nuclear membranes the amount of boundary and trapped phospholipids as well as the amount of cholesterol in trapped lipid domains was greater than that in cortical membranes. Cholesterol was to a large degree excluded from trapped lipid domains in cortical membranes. The difference between the amounts of lipids in domains uniquely formed due to the presence of membrane proteins increased with the donors‘ age. The rigidity of nuclear membranes was greater than that of cortical membranes for all age groups. The nuclear fiber cell plasma membranes were less permeable to oxygen than cortical membranes and both of them become less permeable to oxygen with age. In nuclear porcine membranes the amounts of lipids in domains created due to the presence of membrane proteins were greater than those in cortical membranes and the differences were larger than the differences observed for human membranes. Lipids in porcine nuclear fiber cell membranes were more rigid and less permeable to oxygen than in human nuclear membranes.