Brush border isolated vesicles from

Foscarnet competitively inhibits Na -Pj cotransport in animal and human kidney proximal tubule brush border membrane vesicles, reversibly inhibiting sodium-dependent phosphate transport [48, 49]. Renal cortical Na-K-ATPase and alkaline phosphatase activity are not inhibited by foscarnet, nor is proline, glucose, succinate, or Na" transport [48,49]. Foscarnet induces isolated phosphaturia without hypophosphatemia in thyroparathyroidectomized rats maintained on a low phosphorus diet, without affecting glomerular filtration rate, urinary adenosine 3 5 -cyclic monophosphate (cAMP) activity, or urinary calcium, sodium or potassium excretion [48,50]. Sodium-Pj cotransport in brush border membrane vesicles from human renal cortex was reported to be even more sensitive to inhibition by foscarnet than in rat renal brush border membrane vesicles [49]. 

Gunshin, H., Noguchi, T., and Naito, H. (1991). Effect of calcium on the zinc uptake by brush border membrane vesicles isolated from the rat small intestine. Agric. Biol. Client. 55, 2813-2816. 

Miirer, H Hopfer, U., Kinne, R. (1976). Sodium/proton antiport in brush border membrane vesicles isolated from rat small intestine and kidney. Biochem. J. 154,597-604. 

Vendeland, S.C., Deagen, J.T., Butler, J.A., and Whanger, P.D. 1994. Uptake of selenite, selenomethionine and selenate by brush border membrane vesicles isolated from rat small intestine. BioMetals 7, 305 - 312. 

In addition to the vascular perfusion system studies, we have employed brush border membrane vesicles. Isolated from rat mucosa, to determine more closely the parameters of mucosal zinc transport (43). These vesicle preparations represent the best means currently available to delineate the characteristics of zinc transfer into mucosal cells. The technique permits isolation of the microvillous membrane free of other cellular contaminants, as determined by established procedures (44). 

The studies reported here using the isolated, vascularly perfused rat intestine system and isolated brush border membrane vesicles fail to support a role for a specific zinc-binding ligand involved in zinc uptake in the rat. Rather, the extent of zinc uptake involves the interaction of several phenomena, including both extracellular and intracellular reactions. It appears that the major pathway of zinc uptake under normal dietary conditions involves the transfer of zinc from various dietary components to a carrier mediated transport system at the brush border membrane. The net absorption of zinc from the lumen could involve a competition between various dietary components, zinc binding ligands and the membrane carrier for zinc. Thus, in some cases, those compounds in the lumen with a higher affinity for zinc than the membrane component will be less likely to permit transfer of zinc to the carrier, while compounds with a lower affinity for zinc will increase the amount of zinc made... 

Absorption, Transportation, and Distribution Rubidium is very well absorbed from the alimentary tract of animals (Schafer and Forth 1983), with absorption in humans exceeding 60% in both sexes (Table 1.4-5). Rubidium resembles potassium in its pattern of absorption (channels). On the basis of studies with brush border membrane vesicles isolated from the jejuna of rabbits, potassium and rubidium apparently share a transport system. All plant and animal cells are apparently permeable to rubidium ions at rates comparable with those of potassium (Nielsen 1986). It seems that rubidium uses the potassium channels for entering the cell (Clay and Shlesinger 1983, Gallacher et al. 1984). All soft tissues of the body have rubidium concentrations that are high compared with trace elements, with a typical... 

Tacnet F, Watkins DW, Ripoche P. 1990. Studies of zinc transport into brush-border membrane vesicles isolated from pig small intestine. Biochim Biophys Acta 1024 323-330. 

The first reported instances using isolated plasma membrane vesicles to study Na+-coupled transport were derived from brush borders of the small intestine (Murer and Hopfer, 1974 Sigrist-Nelson et al., 1975) and Ehrlich cells (Colombini and Johnstone, 1974). In rapid succession a number of other systems were established to study translocation of many solutes in many animal cell systems (Schuld-iner and Kaback, 1975 Lever, 1977 Hammerman and Sacktor, 1978 Wright et al., 1983 Saieret al., 1988 see also Table 1). 

Isolated renal cell components (cytosol, organelles, membranes) are also commonly used in vitro systems. Renal microsomes and cytosol are useful in examining the renal biotransformation and bioactivation of nephrotoxicants. Since mitochondria are frequently targets for nephrotoxicants, isolated renal mitochondria are also an important model system for determining the toxic mechanism(s) of some compounds. Also, the direct effects of toxicants on renal cell membranes can be studied in vesicles prepared from either the luminal (brush border) or basolateral (antiluminal, peritubular) membrane of renal cortical cells. The use of isolated cell components is helpful in answering specific questions about... 

The isolated brush border vesicles from the plasma membrane of the microvilU is the simplest in vitro system used so far. The interaction of lipid with rabbit intestinal brush border vesicles has been investigated by Proulx et al. [50] who found that PC, phosphatidylethanolamine, cholesterol, diglyceride as well as fatty acids were taken up by vesicles. Barsukov et al. [51] have shown that transfer of PC from PC vesicles to isolated brush border vesicles can occur in the presence of PC-exchange protein. The use of brush border vesicles is an interesting new approach that permits detailed studies of rate of transfer of specific lipids into the plasma membrane of the enterocyte. The model is seriously hmited by the fact that incubation with solutions containing bile salts at a concentration above the critical micellar concentration will result in partial or total solubilization of the membrane vesicles. 

In order to reduce such interferences, successful efforts have been made to isolate the cell membranes, or even their transport-active constituents. One way to achieve this is by preparation of isolated membranes which have a natural tendency to form closed and homogenous vesicles [31,32]. Another approach is by reconstituted systems , i.e. to isolate membrane components involved in specific transport processes, and to incorporate them in artificial lipid membranes, usually liposomes [33,34]. Vesicles have been successfully prepared from various cells and tissues and tested for transport activities. Whenever membranous material has been isolated from other cellular components it tends to form vesicles spontaneously, sometimes with an uniform orientation, right-side-out or inside-out vesicles, respectively. For mixtures of vesicles of the two orientations, methods were developed to separate the two polarities. Furthermore, one can separate vesicles from different cell types or even from different regions of the cell, e.g. brush-border membranes form basal lateral ones [35,36]. 

Gut riboflavin transport systems have been studied by partly isolated segments of the small intestine within an anesthetized animal by an isolated everted gut segment, or by vesicles , prepared from the brush border. ... 

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