Physical properties of the lipid bilayer membrane made of calf lens lipids: EPR spin labeling studies

Abstract

The physical properties of a membrane derived from the total lipids of a calf lens were investigated using EPR spin labeling and were compared with the properties of membranes made of an equimolar 1-palmitoyl-2-oleoylphosphatidylcholine/cholesterol (POPC/Chol) mixture and of pure POPC. Conventional EPR spectra and saturation-recovery curves show that spin labels detect a single homogenous environment in all three membranes. Profiles of the order parameter, hydrophobicity, and oxygen transport parameter are practically identical in lens lipid and POPC/Chol membranes, but differ drastically from profiles in pure POPC membranes. In both lens lipid and POPC/Chol membranes, the lipids are strongly immobilized at all depths, which is in contrast to the high fluidity of the POPC membrane. Hydrophobicity and oxygen transport parameter profiles in lens lipid and POPC/Chol membranes 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. At this position, hydrophobicity increases from the level of methanol to the level of hexane, and the oxygen transport parameter increases by a factor of 2-3. These profiles in POPC membranes are bell-shaped. It is concluded that the high level of cholesterol in lens lipids makes the membrane stable, immobile, and impermeable to both polar and nonpolar molecules.

Structural properties of lipid reconstructs and lipid composition of normotensive and hypertensive rat vascular smooth muscle cell membranes

“…In parallel, membranes prepared from the lipids extracted from the different arteries of the three rat strains, hypertensive or not, were found to be structurally very similar. The fact that our data from reconstituted membranes differ from reports showing increased microviscosity of SHR membranes (2) in intact cell preparations shifts the focus to the role of cell membrane proteins or the protein-lipid rafts in the membrane microenvironment (33,34). Yet, a direct comparison of the reported ESR data (12) with our data is difficult since no ESR spectra are shown in the cited paper that refer only to the calculated parameters.…”

Lipids and the ocular lens

“…Electron spin resonance probe studies have shown that cholesterol contributes to the impermeability of oxygen across lens membranes ( 202,203 ). Maintaining low levels of oxygen is critical to the lens to prevent oxidation and opacifi cation.…”

The liquid-ordered phase in sphingomyelincholesterol membranes as detected by the discrimination by oxygen transport (DOT) method

“…The best monitor of these changes in the l o phase would be the profile of the oxygen transport parameter across the l o phase membranes. In membranes made of a binary mixture of phospholipids and cholesterol, these profiles changed from the bell shape at 30 mol% cholesterol, to the rectangular shape at 50 mol% cholesterol [22,50,51]. It is significant to note that the abrupt increase in the oxygen transport parameter, by a factor of 2-3, which is observed at 50 mol% cholesterol, occurs between the C9 and C10 position, which is approximately where the steroid ring structure of the cholesterol molecule reaches into the membrane.…”