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Lipid membranes vesicular transport

Lipids are transported between membranes. As indicated above, lipids are often biosynthesized in one intracellular membrane and must be transported to other intracellular compartments for membrane biogenesis. Because lipids are insoluble in water, special mechanisms must exist for the inter- and intracellular transport of membrane lipids. Vesicular trafficking, cytoplasmic transfer-exchange proteins and direct transfer across membrane contacts can transport lipids from one membrane to another. The best understood of such mechanisms is vesicular transport, wherein the lipid molecules are sorted into membrane vesicles that bud out from the donor membrane and travel to and then fuse with the recipient membrane. The well characterized transport of plasma cholesterol into cells via receptor-mediated endocytosis is a useful model of this type of lipid transport. [9, 20]. A brain specific transporter for cholesterol has been identified (see Chapter 5). It is believed that transport of cholesterol from the endoplasmic reticulum to other membranes and of glycolipids from the Golgi bodies to the plasma membrane is mediated by similar mechanisms. The transport of phosphoglycerides is less clearly understood. Recent evidence suggests that net phospholipid movement between subcellular membranes may occur via specialized zones of apposition, as characterized for transfer of PtdSer between mitochondria and the endoplasmic reticulum [21]. [Pg.46]

Brain vascular endothelial cells are linked by tight junction proteins creating high-resistance junctions between cells that effectively prevent the movement of hydrophilic substances, including electrolytes, such as Na and K+. Water moves across the lipid bilayer of endothelial cells through simple diffusion and vesicular transport (Tait et al., 2008). However, specialized water channels are formed by molecules called aquaporins (AQPs), which are highly expressed in blood-brain interfaces to facilitate the transport of water across cell membranes. [Pg.127]

Plausible as the above mechanism may seem, it may, however, not be the whole truth. An alternative mechanism is vesicular transport. In chicken intestine it has been shown that the only epithelial organelles that increased in Ca content as a result of calcitriol treatment were the lysosomes." The result lends support to a transport mechanism involving Ca + uptake across the brush-border membrane by endocytic vesicles, fusion of these vesicles with lysosomes, and possibly also delivery of Ca to the basal lateral membrane of the epithelial cell by exocytosis. This process would also explain the vitamin-D-induced alterations in brush-border-membrane lipid compositions as a consequences of preferential incorporation of certain types of lipids into the vesicles. Interestingly, the lysosomes in the chicken studies also contained high levels of calbin-... [Pg.123]

Vesicular transport occurs when a membrane completely surrounds a compound, particle, or cell and encloses it into a vesicle. When the vesicle fuses with another membrane system, the entrapped compounds are released. Endocytosis refers to vesicular transport into the cell, and exocytosis to transport out of the cell. Endocytosis is further classified as phagocytosis if the vesicle forms around particulate matter (such as whole bacterial cells or metals and dyes from a tattoo), and pinocy-tosis if the vesicle forms around fluid containing dispersed molecules. Receptor-mediated endocytosis is the name given to the formation of clathrin-coated vesicles that mediate the internalization of membrane-bound receptors in vesicles coated on the intracellular side with subunits of the protein clathrin (Eig. 10.14). Potocytosis is the name given to endocytosis that occurs via caveolae (small invaginations or caves ), which are regions of the cell membrane with a unique lipid and protein composition (including the protein caveolin-1). [Pg.168]

There are many methods for the measurement of ion transport through membranes. We shall describe here two physical methods that directly measure ion flow in black lipid membranes, large vesicular, and cell membranes as well as a method that works with a large population of vesicles of any size and entrapped fluorescence dyes. [Pg.122]

In order to characterize lipid vesicle membrane transport properties further, we have begun to study the transport of other molecules and test whether correlations might also exist with mechanical compressibility and water permeability. Here, although some data exists for black lipid membranes [33], little attention has so far been paid to the transport of small molecules and ions for giant vesicular membranes (i.e, free of solvent and boundary-support effects) [87] and none using the micropipet technique on single vesicles. The new series of transport studies considers first urea, which is both a water-soluble and membrane-soluble molecule. [Pg.132]

The vesicular transport, now very well exemplified in the case of some glycoproteins. In this case it is also required that membrane lipids be transferred to the plasma membrane during the membrane flow. Which lipids, and how, has not been matter of concern, and the question remains almost entirely unanswered ... [Pg.69]

Morre and coworkers have also developed a cell-free system from rat liver with which the vesicular transport of proteihs between the ER and the GA was reconstituted in vitro. This approach uses the donor membranes (ER) in solution and the acceptor membranes (GA) immobilized on nitrocellulose strips. This system has also been adapted to reconstitute the vesicular transfer of lipids between the ER and the GA in rat liver [3-4]. The reconstitution of the vesicular (i.e. ATP-dependent) transfer of lipids between different plant membrane fractions has also been obtained with spinach [5]. [Pg.213]

In our laboratory, studies of lipid transfer in leek seedlings in vivo, have already shown the existence of a vesicular process for the transfer of phospholipids and particularly of very long chain fatty acid-containing lipids [6]. This process follows the vesicular endoplasmic reticulum- Golgi apparatus- plasma membrane pathway. Using the cell-free system developed by Morre and coworkers, we have reconstituted in vitro the vesicular transfer of some phospholipids between the ER and the GA. This transfer is ATP and cytosol-dependent, is N Ethyl Maleimide and temperature sensitive and specific for the ER as donor and the GA as acceptor. The phospholipids transferred via an ATP-dependent manner in vitro between the ER and the GA were phosphatidylcholine (PC +79%), phosphatidylethanolamine (PE +67%) and phosphatidylserine (PS +123%) [7]. All those results are in favour of a vesicular transport of phospholipids between the ER and the GA of leek seedlings, and brought us to purify these transition vesicles issued from the ER. [Pg.213]


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