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PubMed1993

Role of gangliosides in behavioral and biochemical actions of alcohol: cell membrane structure and function.

Alcohol exerts its pharmacological effects in adult brain by altering the physicochemical properties of cellular plasma membranes. Although alcohol does induce changes in membrane lipid composition, studies to relate these alterations to the development of behavioral tolerance to alcohol and the withdrawal effects have been unsuccessful. Actions of alcohol on developing brain are even more complex. Some of the reported effects include inhibition of embryogenesis, cell migration, and differentiation, including synaptogenesis. Gangliosides have neuroprotective action against a variety of neural insults (e.g., mechanical injury, drug toxicity, or hypoxic insult). This review addresses the role and significance of gangliosides in the CNS pathophysiology of alcohol exposure, as well as the effect of changes in endogenous gangliosides on membrane structure and function. We also describe the role of exogenous gangliosides in prevention of alcohol (acute and/or chronic)-induced CNS (prenatal and postnatal) neurotoxicity through their action on cellular plasma membranes. We propose that ganglioside's neuroprotective effects against alcohol neurotoxicity involve protection and restoration of plasma membrane structure (proteins and lipids) and thereby its function (ionic homeostasis, neurotransmitter receptor-mediated signal transduction). Thus gangliosides may have potential therapeutic use in treatment of alcohol-related problems.

Alcoholism↗
PubMed1982

Physical studies of cell surface and cell membrane structure. Deuterium nuclear magnetic resonance studies of N-palmitoylglucosylceramide (cerebroside) head group structure.

Deuterium Fourier-transform nuclear magnetic resonance spectra of N-palmitoyl[2,3,4,6,6-2H5]glucosylceramide, N-palmitoyl[1-2H]glucosylceramide, N-palmitoyl-[5,6,6-2H3]glucosylceramide, and N-palmitoyl[6,6-2H2]-glucosylceramide have been obtained at 55.3 MHz (corresponding to a magnetic field strength of 8.5 T) for lipids as multilamellar dispersions in excess water at 90 degrees C, above the gel to liquid-crystal phase transition temperature (Tc = 82 degrees C). Spectra were also obtained for these same lipids dispersed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, and cholesterol, all in excess water at 90 degrees C. The results are analyzed in terms of a model in which the lipid undergoes fast axial diffusion, together with a "wobbling" of the polar head group, by mathematical methods similar to those used previously for the choline and ethanolamine head groups in phosphatidylcholines and phosphatidylethanolamines [Skarjune, R., & Oldfield, E. (1979) Biochemistry 18, 5903--5909]. However, contrary to the results obtained in the previous study, which indicated many possible conformations for the choline and ethanolamine head groups, results with labeled cerebrosides yield at most a few orientations for the glucose head group in each of the systems studied. Furthermore, where multiple solutions do occur, they fall within a narrow orientational subspace so that all solutions exhibit the same general features. We also show that the order parameter describing the head group wobble is fully determined for each system, and it indicates a rather mobile structure for the cerebroside head group, in a variety of environments. In each system studied the polar head group projects essentially straight up from the bilayer surface into the aqueous region, thereby permitting maximum hydration of the four glucose hydroxyl groups by bulk water molecules.

Cell Membrane↗
PubMedDate not supplied

[Content and transportation of Ca(2+) to hepatocytes and lipid content of liver cell membrane structure in experimental diabetes in the rat].

It is proved that at experimental diabetes the calcium content in hepatocytes is disturbed. This disorder is mostly shown in increase of calcium content in hepatocytes and in decrease of accumulation of these ions in mitochondrias. One of the possible reasons of changes at this pathology is the change of lipid content of hepatocytes, mitochondrias and microsomes. It is proved that the in vitro model systems Ca ions inhibits the synthesis of 25-hydroxyvitamin D3 by hepatocytes.

Animals↗
PubMed1989

Lipid regulation of cell membrane structure and function.

Recent studies of structure-function relationships in biological membranes have revealed fundamental concepts concerning the regulation of cellular membrane function by membrane lipids. Considerable progress has been made in understanding the roles played by two membrane lipids: cholesterol and phosphatidyl-ethanolamine. Cholesterol has been shown to regulate ion pumps, which in some cases show an absolute dependence on cholesterol for activity. These studies suggest that an essential role that cholesterol plays in mammalian cell biology is to enable crucial membrane enzymes to provide function necessary for cell survival. Studies of phosphatidylethanolamine regulation of membrane protein activity and regulation of membrane morphology led to hypotheses concerning the roles for this particular lipid in biological membranes. New information on lipid-protein interactions and on the nature of the lipid head groups has permitted the development of mechanistic hypotheses for the regulation of membrane protein activity by phosphatidyl-ethanolamine. In addition, intermediates in the lamellar-nonlamellar phase transitions of membrane systems containing phosphatidylethanolamine, or other lipids with similar properties, have recently been implicated in facilitating membrane fusion. Finally, studies of transmembrane movement of lipids have provided new insight into the regulation of membrane lipid asymmetry and the biogenesis of cell membranes. These kinds of studies are harbingers of a new generation of progress in the field of cell membranes.

Animals↗
PubMed1979

Physical studies of cell surface and cell membrane structure. Determination of phospholipid head group organization by deuterium and phosphorus nuclear magnetic resonance spectroscopy.

Phospholipid head group conformations in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE), DPPC-cholesterol, and DPPE-cholesterol dispersions, in excess water above the pure lipid gel to liquid-crystal phase transition temperature, have been calculated by using comparisons between experimental 2H and 31 P NMR spectral parameters and theoretical results obtained from a plausible model of head group motions. The new calculations are compared with results obtained in previous studies [Seelig, J., Gally, H. U., & Wohlgemuth, R. (1977) Biochem, Biophys. Acta 467, 109--117; Brown, M. F. & Seelig, J. (1978) Biochemistry 17, 381--384; Seelig, J., & Gally, H. U. (1976) Biochemistry 15, 5199--5204] and are shown to agree qualitatively under certain highly restrictive conditions. Under more general conditions, it is shown that many possible solutions are generated but that these may often be separated into a small number of likely conformations in which the head group torsion angles are restricted to specific ranges rather than to a discrete set of values. There is no NMR evidence, however, to support the notion that there are only single conformational solutions to the NMR measurements for the above phospholipid systems.

Cell Membrane↗
PubMed1979

Physical studies of cell surface and cell membrane structure. Deuterium nuclear magnetic resonance investigation of deuterium-labelled N-hexadeconoylgalactosylceramides (cerebrosides).

1. Deuterium Fourier transform nuclear magnetic resonance spectra of a series of N-palmitoylgalactosylceramides (cerebrosides) specifically labelled with deuterium at one of positions 2', 6', 10' and 16' of the acyl chain, or in the C-6 hydroxymethyl group of the galactose residue, have been obtained using a spin-echo technique at 34.1 MHz with a homebuilt superconducting magnet spectrometer. 2. The effects of temperature and cholesterol on the deuterium spectra have been investigated. The results indicate, when compared at the same reduced temperature, that the hydrocarbon chain organization in the liquid crystalline phase of palmitoylgalactosylceramide is essentially identical to that seen in similar chain length glycerophospholipids. In particular, two sets of quadrupole splittings are seen for a 2'-labelled N-palmitoylgalactosylceramide, indicating non-equivalent deuterons as noted previously for phospholipids. 3. Two sets of quadrupole splittings are observed for the headgroup C-6-labelled N-palmitoylgalactosylceramide. It is proposed that these signals arise from the enantiomeric R and S lipids, and that motion of the hydroxymethyl group is slow (greater than 10(-5) S). These results suggest the presence of a hydrogen bond network in the polar headgroup region. 4. The effects of cholesterol on the deuterium spectra of N-palmitoylgalactosylceramide-labelled as C2H3 in the terminal methyl group, at 1:1 mol ratios and in excess water below the crystal to liquid-crystal phase transition temperature (Tc) of the pure lipid (82 degrees C), are different to the effects seen with the phosphatidylcholine-cholesterol system. The spectra below Tc are characterised by two overlapping powder patterns, one with a quadrupole splitting of approx. 6 kHz (fluid liquid-crystalline phase) and one with a quadrupole splitting of about 20--25 kHz (crystal or gel-state lipid). Exchange between these two environments is therefore slow, leading to the possibility of characterising the cerebroside-cholesterol phase diagram using deuterium nuclear magnetic resonance spectroscopy.

Cell Membrane↗
PubMed1985

Working at higher magnifications in scanning electron microscopy with secondary and backscattered electrons on metal coated biological specimens and imaging macromolecular cell membrane structures.

Membrane structures of macromolecular dimensions were imaged with high resolution secondary electron type I (SE-I) signal contrasts on metal coated biological specimens. The quality of the surface information was strongly dependent on the signal used for microscopy and on the properties of metal films, i.e., thickness, continuity, structure and decoration effects. Films of 10 nm thickness produced so much type II electrons that identical images were obtained with the conventional SE-II and BSE-II signals. In such images, the type I SE signal was so low that only very weak contrasts were recognizable. If the films--continuous or discontinuous--were composed of large metal aggregates (gold and platinum) a strong micro-roughness contrast was produced by the type II signal. At high magnifications (100,000 x) this background signal greatly reduced the S/N ratio of the SE-I signal. A similar effect was previously shown to be produced by the type III background signal. The type II background signal minimized when continuous films of small aggregates (tantalum and chromium) were applied. SE-I contrast dominated in the image if the film thickness was limited to 1 nm. Additionally, it was found that gold and platinum decorated membrane surface structures, less than 20 nm in size, and did not reveal all the topographic information available (size, shape, orientation spacing of small surface features) but merely displayed center-to-center distances. These decoration effects were avoided and extensive topographic information was obtained through surface coating with Ta or Cr.

Animals↗
PubMedDate not supplied

Membrane switch hypothesis. 1. Cell density influences lateral domain structure of tumor cell membranes.

The domain structure of human cancer cells membranes was investigated by electron paramagnetic resonance (EPR) in different phases of cell growth, and the results were compared to those obtained for nonmalignant cells. On the basis of computer simulation of the EPR spectra using a newly developed GHOST condensation routine it was suggested that plasma membranes of cancer cells have less lateral lipid domain types at confluent conditions than in the exponential growing phase, while in nonmalignant cells the domain structure does not change significantly during cell growth. In accordance to our experimental data we propose a membrane switch hypothesis: disappearance of certain membrane domain types might act as a switch promoting the clustering of membrane constituents into the active units in a common lipid membrane domain and thus influencing the physiology of cells.

Cell Count↗
PubMed1973

Changes in membrane structure associated with cell contact.

Ultrastructural analysis of 3T3 fibroblasts by freeze-cleavage has demonstrated significant changes in cell-membrane structure associated with cell-to-cell contact and malignant transformation. These changes consist of a rearrangement and redistribution of intramembranous particles on the membrane fracture faces exposed by freeze-cleavage. The results show that noncontacted 3T3 cells in low density contain randomly distributed intramembranous particles. With the development of cell-to-cell contacts during the logarithmic phase of growth however, a pronounced aggregation of intramembranous particles is seen. A direct correlation between the degree of cell contact and the percentage of cells showing intramembranous-particle aggregation has been established. By contrast, transformed SV3T3 and SP3T3 cells show no evidence of intramembranous-particle aggregation even at cell densities where cell-to-cell contact is extensive. In view of recent reports that intramembranous particles represent foci of interaction between certain intrinsic membrane proteins and lipids, we propose that cell-to-cell contact of nontransformed 3T3 cells may initiate a change in the distribution of intrinsic membrane proteins associated with intramembranous particles and that these changes may influence control of cell proliferation.

Animals↗
PubMed2001

Electrostatics of cell membrane recognition: structure and activity of neutral and cationic rigid push-pull rods in isoelectric, anionic, and polarized lipid bilayer membranes.

Design, synthesis, and structural and functional studies of rigid-rod ionophores of different axial electrostatic asymmetry are reported. The employed design strategy emphasized presence of (a) a rigid scaffold to minimize the conformational complexity, (b) a unimolecular ion-conducting pathway to minimize the suprastructural complexity and monitor the function, (c) an extended fluorophore to monitor structure, (d) variable axial rod dipole, and (e) variable terminal charges to create axial asymmetry. Studies in isoelectric, anionic, and polarized bilayer membranes confirmed a general increase in activity of uncharged rigid push-pull rods in polarized bilayers. The similarly increased activity of cationic rigid push-pull rods with an electrostatic asymmetry comparable to that of alpha-helical bee toxin melittin (positive charge near negative axial dipole terminus) is shown by fluorescence-depth quenching experiments to originate from the stabilization of transmembrane rod orientation by the membrane potential. The reduced activity of rigid push-pull rods having an electrostatic asymmetry comparable to that in alpha-helical natural antibiotics (a positive charge near the positive axial dipole terminus) is shown by structural studies to originate from rod "ejection" by membrane potentials comparable to that found in mammalian plasma membranes. This structural evidence for cell membrane recognition by asymmetric rods is unprecedented and of possible practical importance with regard to antibiotic resistance.

Amino Acid Sequence↗
PubMed1991

[Free radical oxidation of red blood cell membrane lipid structures as a trigger mechanism of an increase in red blood cell membrane permeability during blood coagulation in vitro].

The study of venous blood samples from 50 clinically normal subjects has shown that free radical oxidation of red blood cell membrane lipid structure induced by the blood sample contact with atmospheric oxygen serves a trigger rising the membrane permeability during blood coagulation in vitro. Activation of endogenous phospholipase A2 is a process dependent on the increase of intraerythrocytic concentration of calcium ions.

Blood Coagulation↗
PubMed1978

[Topical immunochemical consideration of the structure of the tumour cell membrane (author's transl)].

Fundamental experiments and results in the elucidation of cell membrane structure are reviewed in detail. Special consideration is given to the topochemical organisation and immunochemistry of the glycolipids and glycoproteins that are integrated into the cell membrane, and which form a major component of the surface receptor mosaic. This, in turn, underlies a transmembrane, cytoskeletal control, a mechanism that can only be explained by the modern concept of a fluid membrane. The investigations discussed here provide an interpretation of the behaviour and properties of the membranes of the tumour cell, as observed in the effect of cell transformation on the topography of the plasma membrane, and during the cell cycle and cell growth. In this connection, the so-called tumour associated antigens are discussed fully and their biochemistry and immunology treated in detail. Concepts of tumour immunity and escape mechanisms are then elucidated and defined with the aid of model systems. Using examples, it is shown why the results of this fundamental research form a sound basis for the immunodiagnosis and therapy of tumours.

Animals↗
PubMed1991

Dietary fat: exogenous determination of membrane structure and cell function.

Evidence indicates that principal features of the membrane involve structural organization of lipids in the form of a bilayer with functional proteins either bound to the bilayer surface or inserted into the bilayer and interacting within specific domains in the lipid milieux. In homeotherms, intrinsic and extrinsic factors apparently form the basis for determination of membrane lipid composition and thus membrane physicochemical properties. Moreover, many intrinsic metabolic controls, such as fatty acid desaturation and phospholipid biosynthesis, may be attenuated by change in the nature of the extrinsic or dietary influence. This review will focus on the role of dietary fat as a determinant of subcellular structural constituents to illustrate that feeding nutritionally adequate diets differing in fatty acid composition can induce physiological transitions in membrane function involving the activity of enzymes responsible for synthesis of membrane constituents, hormone-activated functions and expression of activity in the cell nucleus.

Animals↗
PubMed1976

Protein-liposome interactions and their relevance to the structure and function of cell membranes.

Recent studies on the interactions of soluble proteins, membrane proteins and enzymes with phospholipid model membranes are reviewed. Similarities between the properties of such systems and the behavior of biomembranes, such as alterations in the redox potential of cytochrome c after binding to membranes and effects of phospholipid fluidity on (Na+K) ATPase activity, are emphasized. The degree of correspondence between the behavior of model systems and natural membranes encourages the continuing use of model membranes in studies on protein-lipid interactions. However, some of the data on the increase of surface pressure of phospholipid monolayers by proteins and increases in the permeability of liposomes indicate that many soluble proteins also have a capability to interact hydrophobically with phospholipids. Thus a sharp distinction between both peripheral and integral membrane proteins and non-membrane proteins are not seen by these techniques. Cautious use of such studies, however, should lead to greater understanding of the molecular basis of cell membrane structure and function in normal and pathological states. Studies implicating protein-lipid interactions and (Na+K) ATPase activity in membrane alterations in disease states are also briefly discussed.

Adenosine Triphosphatases↗
PubMed1975

The structure of cell membranes involved in intercellular communication.

The molecular structure of mouse hepatocyte gap junctions is investigated with corrlated electron microscopy, biochemistry, and x-ray diffraction technics. These studies reveal that the gap junction is composed of a hexagonal lattice of protein subunits, connexons, which pierce the hydrophobic membrane and establish a structural basis for intercellular hydrophilic channels or pores. By digesting liver-cell membranes with trypsin, a preparation of open- and closed-gap junction vesicles can be generated; this preparation will permit direct permeability measurements across the gap junction membranes in an in-vitro system.

Animals↗