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Articles 451 - 455 of 455

Full-Text Articles in Dentistry

Ph-Sensitive Liposomes Mediate Cytoplasmic Delivery Of Encapsulated Macromolecules, Robert M. Straubinger, Nejat Düzgüneş, Demetrios Papahadjopoulos Jan 1985

Ph-Sensitive Liposomes Mediate Cytoplasmic Delivery Of Encapsulated Macromolecules, Robert M. Straubinger, Nejat Düzgüneş, Demetrios Papahadjopoulos

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Negatively charged liposomes are endocytosed by the coated vesicle system and accumulate in acidic intracellular vesicles. Liposomes that become unstable at acidic pH improve cytoplasmic delivery of membraneimpermeant macromolecules such as calcein (CAL) and FITC dextran (18 or 40 kDa). Oleic acid (OA): phosphatidylethanolamine (PE) (3:7 mole ratio) liposomes become permeable to CAL at pH < 7.0. Control liposomes of phosphatidylserine : PE or OA : phosphatidylcholine are stable at pH 4-8. OA:PE liposomes promote cytoplasmic delivery of encapsulated CAL to CV-1 cells, as evidenced by the emergence of diffuse, cytoplasmic CAL fluorescence. Delivery requires metabolic energy and is partially inhibited by chloroquine or monensin, which raise the pH of intracellular vesicles. © 1985.

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Interaction Of Phosphatidylserine-Phosphatidylcholine Liposomes With Sickle Erythrocytes. Evidence For Altered Membrane Surface Properties, R. S. Schwartz, Nejat Düzgüneş, D. Tsun Yee Chiu, B. Lubin Jan 1983

Interaction Of Phosphatidylserine-Phosphatidylcholine Liposomes With Sickle Erythrocytes. Evidence For Altered Membrane Surface Properties, R. S. Schwartz, Nejat Düzgüneş, D. Tsun Yee Chiu, B. Lubin

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The sickle erythrocyte (RBC) is a pathologic RBC that contains multiple membrane abnormalities. Some of these abnormalities have been implicated in the pathophysiology of vasoocclusive crises characteristic of sickle cell disease; others have yet to be defined in terms of their clinical significance. Recent information has shown that sickle RBC adhere abnormally to cultured endothelial cells yet little is known about the ways in which sickle cells interact with model membranes of defined size and lipid composition. We investigated this phenomenon by interacting sickle RBC with artificial lipid vesicles (liposomes) containing acidic phospholipids. Our results demonstrate that sickle disease (hemoglobin …

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Fusion Of Phospholipid Vesicles Arrested By Quick-Freezing. The Question Of Lipidic Particles As Intermediates In Membrane Fusion, E. L. Bearer, Nejat Düzgüneş, Daniel S. Friend, Demetrios Papahadjopoulos Dec 1982

Fusion Of Phospholipid Vesicles Arrested By Quick-Freezing. The Question Of Lipidic Particles As Intermediates In Membrane Fusion, E. L. Bearer, Nejat Düzgüneş, Daniel S. Friend, Demetrios Papahadjopoulos

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We have examined the early events in Ca2+-induced fusion of large (0.2 μm diameter) unilamellar cardiolipin/phosphatidylcholine and phosphatidylserine/phosphatidylethanolamine vesicles by quick-freezing freeze-fracture electron microscopy, eliminating the necessity of using glycerol as a cryoprotectant. Freeze-fracture replicas of vesicle suspensions frozen after 1-2 s of stimulation revealed that the majority of vesicles had already undergone membrane fusion, as evidenced by dumbbell-shaped structures and large vesicles. In the absence of glycerol, lipidic particles or the hexagonal HII phase, which have been proposed to be intermediate structures in membrane fusion, were not observed at the sites of fusion. Lipidic particles were evident in less …

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Synexin Facilitates Fusion Of Specific Phospholipid Membranes At Divalent Cation Concentrations Found Intracellularly., K. Hong, Nejat Düzgüneş, R. Ekerdt, Demetrios Papahadjopoulos Jan 1982

Synexin Facilitates Fusion Of Specific Phospholipid Membranes At Divalent Cation Concentrations Found Intracellularly., K. Hong, Nejat Düzgüneş, R. Ekerdt, Demetrios Papahadjopoulos

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The effect of synexin (an adrenal medullary protein) on the kinetics of Ca2+- and Mg2+-mediated membrane fusion was examined. Membrane fusion was studied by monitoring intermixing of the aqueous contents of phospholipid vesicles. Synexin facilitated Ca2+-mediated, but not Mg2+-mediated, fusion of phosphatidate/phosphatidylethanolamine (1:3) and phosphatidate/phosphatidylserine/phosphatidylethanolamine/cholesterol (1:2:3:2) vesicles. The threshold concentration of Ca2+ for fusion was decreased to approximately equal to 10 microM in the presence of synexin at 6 micrograms/ml and 1.5 mM Mg2+ in vesicle suspensions containing 50 microM lipid. This effect of synexin was drastically inhibited by including 25% phosphatidylcholine (mol/mol) in the vesicle membrane. It is proposed …

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Modulation Of Membrane Fusion By Calcium-Binding Proteins, K. Hong, Nejat Düzgüneş, Demetrios Papahadjopoulos Jan 1982

Modulation Of Membrane Fusion By Calcium-Binding Proteins, K. Hong, Nejat Düzgüneş, Demetrios Papahadjopoulos

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The effects of several Ca2+-binding proteins (calmodulin, prothrombin, and synexin) on the kinetics of Ca2+-induced membrane fusion were examined. Membrane fusion was assayed by following the mixing of aqueous contents of phospholipid vesicles. Calmodulin inhibited slightly the fusion of phospholipid vesicles. Bovine prothrombin and its proteolytic fragment 1 had a strong inhibitory effect on fusion. Depending on the phospholipid composition, synexin could either facilitate or inhibit Ca2+-induced fusion of vesicles. The effects of synexin were Ca2+ specific. 10 microM Ca2+ was sufficient to induce fusion of vesicles composed of phosphatidic acid/phosphatidylethanolamine (1:3) in the presence of synexin and 1 mM …

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