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  • 1
    Electronic Resource
    Electronic Resource
    Endothelium, the dynamic interface in cardiac lipid transport (1992)
    Springer
    Molecular and cellular biochemistry 116 (1992), S. 181-191 
    Details
    ISSN: 1573-4919
    Keywords: fatty acid transport ; monoacylglycerol transport ; lipoprotein lipase ; insulin ; lipolysis ; cell membranes ; plasma triacylglycerol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Vascular endothelium is the dynamic interface in transport of lipid from blood to myocytes in heart and arteries. The luminal surface of endothelium is the site of action of lipoprotein lipase on chylomicrons and VLDL and the site of uptake of fatty acids from albumin. Fatty acids and monoacylglycerols are transported from the lumen in an interfacial continuum of endothelial and myocyte membranes. Lipoprotein lipase is transferred from myocytes to the vascular lumen, and is anchored there, by proteoheparan sulfate in cell membranes. Insulin, needed for synthesis of lipoprotein lipase and esterfication of fatty acids, is captured from the blood stream and delivered to myocytes by endothelial insulin receptors. Fatty acids, monoacylglycerols, lipoprotein lipase and insulin are transported along the same route, but by different mechanisms. The route involves the plasma membrane of endothelium and myocytes, the membrane lining transendothelial channels, and intercellular contacts. (Mol Cell Biochem116: 181–191, 1992)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01270586
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  • 2
    Electronic Resource
    Electronic Resource
    Milk lipid absorption and chylomicron production in the suckling rat (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 195 (1979), S. 397-412 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Structural correlates of milk lipid absorption and chylomicron production were studied in 10-day-old suckled rats. The gastric and duodenal contents and duodenal mucosae were examined with the light and electron microscopes. In the gastric lumen the milk lipid globule cores were smooth, circular and uniformly electron opaque. Many membranes and lamellar structures with a trilaminar and multilamellar appearance were adherent to the peripheries of the cores. In the central duodenal lumen the milk lipid globule cores were also smooth, circular and uniformly electron opaque. Very few milk lipid globules in the duodenal lumen showed adherent membranes or lamellae. Membrane fragments and lamellae were present in the lumen separate from the milk lipid globules. In the duodenal lumen between villi the milk lipid globules had multiple electron lucent indentations of the core. It is believed that the irregular peripheries of the milk lipid globule cores are the result of lipolysis within the duodenal lumen acting at the milk lipid globule surface. This lipolysis of triacylglycerol would produce amphiphilic lipids which may result in the electron lucent spaces at the milk lipid globule periphery. The absorptive epithelial cells along the length of the duodenal villus varied in structure relative to their position at the tip, middle, or base of the villus. Typical mid-villus epithelial cells contained lipid droplets averaging 0.3-μm diameter in the smooth and rough endoplasmic reticulum and in Golgi complexes in the apical cytoplasm. Villus tip and villus base cells contained large lipid droplets between 7-16 μm. Only a few 0.3-μm lipid droplets were present within these cells. These large lipid droplets appeared to be accumulations of triacylglycerol present in the apical cytoplasm associated with lamellar and membranous structures. Numerous chylomicrons were present between epithelial cells located in the middle region of the villus while significantly fewer chylomicrons were seen between epithelial cells at the tip and base of the villus. These observations suggest that the cells at the middle of the duodenal villus of suckling rats were more efficient in the production of chylomicron triacylglycerol derived from incoming milk triacylglycerol than cells at the tip and base of the villus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1091950301
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  • 3
    Electronic Resource
    Electronic Resource
    Scanning electron microscopic study of chylomicrons incubated with lipoprotein lipase (1976)
    New York, NY [u.a.] : Wiley-Blackwell
    The @Anatomical Record 184 (1976), S. 599-609 
    Details
    ISSN: 0003-276X
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effects of lipolysis on the structure of chylomicrons were studied with the scanning electron microscope using rat chylomicrons incubated with purified bovine milk lipoprotein lipase for 20 minutes at pH 8.1. Since the amount of albumin added to the medium was limited, some of the free fatty acids and partial glycerides formed by lipolysis accumulated in the chylomicrons. Lipolyzed chylomicrons fixed with OsO4 at pH 7.4 appeared in scanning electron micrographs as spheres with multiply indented irregular surfaces, while those fixed at pH 5.5, as well as control chylomicrons fixed at both pHs, appeared as spheres with smooth surfaces. Sections of OsO4-fixed specimens, viewed with the transmission electron microscope, showed that the core of lipolyzed chylomicrons fixed at pH 7.4 contained numerous circular electron-lucent areas at the periphery, thus accounting for the indented surfaces observed above, while the core surfaces of the other specimens were circular and smooth. These findings confirm an earlier report that aqueous spaces form in chylomicrons during lipolysis when albumin in the medium is limited, and that the aqueous spaces disappear when specimens are prepared at pH 5.5 for microscopy. Thin sections of specimens that had been prepared for scanning electron microscopy showed that the gold-palladium coating was deposited directly on the indented surface of the lipid core of lipolyzed chylomicrons fixed at pH 7.4. It is concluded that vacuum dehydration during specimen preparation ruptures the outer wall of the aqueous spaces in lipolyzed chylomicrons and thereby exposes the interior of the spaces to gold-palladium coating and viewing with the scanning electron microscope.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ar.1091840402
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  • 4
    Electronic Resource
    Electronic Resource
    Lipolysis of serum-activated triacylglycerol at the surface of J774.1 macrophages (1986)
    Springer
    Cell & tissue research 244 (1986), S. 95-105 
    Details
    ISSN: 1432-0878
    Keywords: Fatty acid ; Lamellar structures ; Lipoprotein lipase activity ; Monoacylglycerol ; Myelin figures ; Murine macrophages
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cultured mouse (J774.1) macrophages accumulated triacylglycerol, but no cholesteryl ester or cholesterol, when incubated in albumin-poor medium with serum-activated lipid particles containing 84 mol% trioleoylglycerol and 9 mol% cholesteryl oleate. Accumulation of triacylglycerol by cells was associated with hydrolysis of particulate triacylglycerol to fatty acid and glycerol. Both acyl and glyceryl moieties of particulate triacylglycerol were recovered in cellular triacylglycerol with a molar ratio of 3.6. The cells also accumulated fatty acid and monoacylglycerol. Whether acylglycerol was taken up as a single molecular species, such as monoacylglycerol, or as several species can not be determined by the present findings. Macrophages incubated with lipid particles for 24 h had many lipid particles attached to cell surfaces and numerous intracellular lipid droplets. The surface film of attached particles was continuous with the outer leaflet of plasma membrane of the cells. Particles partially depleted of core triacylglycerol and collapsed surface films were found attached to surfaces of macrophages. There was no morphological evidence that lipid particles were taken up intact by cells, through endocytosis or phagocytosis. Macrophages incubated with lipid particles also contained intracellular lamellar structures. They varied in size and shape, and were located in the periphery of cells, sometimes near lipid droplets and endoplasmic reticulum. Only 3% of the lamellar structures were associated with lysosomes, indicating they probably were not of lysosomal origin. Lipid particles attached to cells decreased in size and number, and lamellar structures developed at the surface of particles, or replaced the particles, when glutaraldehyde-fixed specimens were incubated at 25° C, demonstrating lipolytic activity at the surface of macrophages. Our findings suggest that particulate triacylglycerol was hydrolyzed by lipoprotein lipase at the surface of macrophages, and that fatty acid and monoacylglycerol formed by lipolysis were transported directly into the cells to be reesterified. When lipolytic products were taken up faster than they could be utilized, they accumulated as lamellar structures in the cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00218386
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  • 5
    Electronic Resource
    Electronic Resource
    Demonstration of fatty acid domains in membranes produced by lipolysis in mouse adipose tissue (1986)
    Springer
    Cell & tissue research 246 (1986), S. 495-508 
    Details
    ISSN: 1432-0878
    Keywords: Fatty acids ; Cell membranes ; Adipose tissue ; Lipolysis ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Fatty acids produced by isoproterenol-stimulated lipolysis in mouse adipose tissue incubated at pH 7.4 formed myelin figures when the tissue was processed at pH 9.0. Myelin figures, visualized with freeze-fracture electron microscopy, were found in intracellular channels of adipocytes, extracellular space, intracellular channels of endothelial cells, and capillary lumen. The E-fracture face of plasma membranes of adipocytes and endothelial cells and intracellular membranes of adipocytes contained areas that were free of particles. These areas, which were continuous with particle-studded areas of the E-fracture faces, were irregular in shape, sometimes circular or oblong, other times long and narrow. The surfaces of particle-free areas were flat, concave, convex, and often corrugated, with multiple folds that sometimes abutted on myelin figures. We conclude that the particle-free areas are composed of partially ionized fatty acids located in the external leaflets of plasma and intracellular membranes of adipocytes and endothelium. They were formed by fatty acids that entered leaflets at pH 9.0, probably from lipolyzed lipid droplets in adipocytes, moved in a continuum of membrane leaflets between and within cells, overcrowded the leaflets, and subsequently produced corrugations and lamellar extensions (myelin figures) of leaflets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00215189
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  • 6
    Electronic Resource
    Electronic Resource
    Cytochemical studies of lipid metabolism: Immunogold probes for lipoprotein lipase and cholesterol (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 185 (1989), S. 255-263 
    Details
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: In this article, cytochemical methods are presented for the study of lipid metabolism both in normal cells and in mutant cells with genetic disorders characterized by abnormal lipid metabolism. The benefit of using an immunocytochemical approach to the study of lipase in tissues is discussed, and a review is presented of the results on immunolocalization of lipoprotein lipase in cardiac tissue of normal mice. Immunocytochemical techniques are applied to the study of lysosomal proliferation in hepatocytes from liver of mutant mice with a genetic defect responsible for the lack of hepatic lipase and lipoprotein lipase activity in these animals. Localization of lipids in tissues with structural techniques has been an area of great interest to our laboratory for many years. Attention is called to the development of a technique for the visualization of fatty acids as a function of their ionization state and the production of fatty-acid myelin figures in membranes. Results on the use of filipin to detect unesterified cholesterol in membranes are reviewed. Filipin produces fluorescent filipin-cholesterol complexes but also perturbs cell membranes. Application of this cytochemical probe, in combination with immunocytochemistry of lysosomes, produced useful information on defects in low-density lipoprotein-derived cholesterol translocation in mutant human fibroblasts. Initial results on the application of immunological techniques to the study of cholesterol in lipid model systems indicate a novel approach, which may be applicable to specialized cell systems. Recent advances in cryoultramicrotomy and development of immunoprobes present valuable opportunities for the structural assessment of lipids and lipases in cell organelles and cell membranes.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aja.1001850218
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  • 7
    Electronic Resource
    Electronic Resource
    Electron microscopic visualization of fatty acids in tissues (1987)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 7 (1987), S. 205-221 
    Details
    ISSN: 0741-0581
    Keywords: Lamellar structures ; Myelin figures ; Lipoprotein lipase ; Triacylglycerol ; Adipose tissue ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Long-chain fatty acids are important structural and metabolic functions in tissues. Fatty acids are derived from triacylglycerol-rich particles in capillaries (chylomicrons and very-low-density lipoproteins) and from triacylglycerol stored in cells (lipid droplets) by the hydrolytic activity of tissue lipases.The identification and localization of fatty acids in tissues has been considered difficult to obtain by using conventional ultrastructural techniques. However, structural findings from our studies on fatty acid transport in tissue became interpretable due to the use of many overlapping techniques. We present here these ultrastructural techniques developed to study fatty acids in tissues and review data which demonstrate lipase activity and fatty acid production from triacylglycerol in aldehyde-fixed tissue. Accumulations of fatty acid in tissue are present as lamellar structures with periodicity of 40-50 Å in sections of resin-embedded tissue and as hydrated myelin figures in freeze fracture replicas of unfixed and fixed tissue. Finally, a new method, using the ionization properties of fatty acids combined with freeze fracture, locates these amphipathic molecules to leaflets of membrane bilayers.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060070310
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