Physical properties of the lipid bilayer membrane made of cortical and nuclear bovine lens lipids: EPR spin-labeling studies

Abstract

The physical properties of membranes derived from the total lipids extracted from the lens cortex and nucleus of a two-year-old cow 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 cortical lipids. Properties of these membranes are very similar to those reported by us for membranes made of the total lipid extract of six-month-old calf lenses (J. Widomska, M. Raguz, J. Dillon, E. R. Gaillard, W. K. Subczynski, Biochim. Biophys. Acta 1768 (2007) 1454–1465). However, in membranes made from nuclear lipids, two domains were detected by the EPR discrimination by oxygen transport method using the cholesterol analogue spin label and were assigned to the bulk phospholipid-cholesterol domain (PCD) and the immiscible cholesterol crystalline domain (CCD), respectively. Profiles of the order parameter, hydrophobicity, and the oxygen transport parameter are practically identical in the bulk PCD when measured for either the cortical or nuclear lipid membranes. In both membranes, lipids in the bulk PCD 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 permeability coefficient for oxygen, estimated at 35°C, across the bulk PCD in both membranes is slightly lower than across the water layer of the same thickness. However, the evaluated upper limit of the permeability coefficient for oxygen across the CCD (34.4 cm/s) is significantly lower than across the water layer of the same thickness (85.9 cm/s), indicating that the CCD can significantly reduce oxygen transport in the lens nucleus.

Properties of membranes derived from the total lipids extracted from clear and cataractous lenses of 61–70-year-old human donors

“…For all these membranes the oxygen transport parameter from the membrane surface to the depth of C9 is as low as in gel-phase PC membranes; at locations deeper than the C9 it is as high as in fluid-phase membranes (Subczynski et al 1989, 1991). These profiles are typical for liquid-ordered-phase membranes saturated with Chol and are very different from the bell-shaped profile across model membranes without Chol (Mainali et al 2012b; Raguz et al 2008, 2009; Subczynski et al 2010; Widomska et al 2007). Similar to profiles of the order parameter (Fig.…”

“…We are concerned with cholesterol-induced changes in the properties and organization of the lipid bilayer of the fiber cell plasma membrane. We have investigated membranes with lipid compositions resembling those of the eye lenses of different species (Mainali et al 2012a, 2013b; Raguz et al 2009) and lens-lipid membranes formed from lipids extracted from the eyes of different species, donors of different age, and different regions of the eye lens (Mainali et al 2012a, 2013b; Raguz et al 2008, 2009; Widomska et al 2007). Previous research, summarized in a review by Subczynski et al (2012), has enabled identification of a substantial number of cholesterol functions specific to the fiber cell plasma membrane.…”

α- and β-Crystallins Modulate the Head Group Order of Human Lens Membranes during Aging

“…Recent data from Raguz et al 49 indicate that lipid bilayer membranes made of lipids extracted from lenses are completely in a liquid-ordered phase. Although the techniques used were different from those used here, this finding may suggest that in the lens, the properties of the cell membranes are markedly affected by the presence of other components, including extrinsic proteins.…”

Spin-label W-band EPR with Seven-Loop–Six-Gap Resonator: Application to Lens Membranes Derived from Eyes of a Single Donor

“…Fatty acids are mainly saturated or monounsaturated, and phospholipids of young animals contain ~33% palmitate, ~33% oleate, and ~10% nervonate [36]. These membranes contain extremely high amounts of cholesterol, which not only saturate the phospholipid bilayer but also induce formation of pure cholesterol bilayer domains (CBDs) within the phospholipid bilayer (PCD) [19, 20]. Co-existence of these domains creates the possibility for partitioning of lipid spin-labels.…”

“…Lipids were derived from eyes of different species [18–20], from donors of different age [18–22], and from different regions of the eye lens, namely the cortex and nucleus [18–20]. These studies were summarized in a review [23].…”