Intracellular transport/distribution

A combinatorial library of fluorescent NBD molecules was used to visualize subcellular transport pathways in living cells, using a kinetic, high content imaging system to monitor spatiotemporal variations of intracellular probe distribution <2004MI414>. 

Prenatal diagnosis of I-cell disease has been based on greatly reduced phosphotransferase activity (cf. Biochemical Perspectives section) and abnormal intracellular-extracellular distribution of lysosomal enzymes in cultured amni-otic fluid cells (Table 17-3).As indicated in Table 17-3, amniotic fluid cells secrete large amounts of lysosomal enzymes into the extracellular medium. Decreased levels of lysosomal enzymes in chorionic villi obtained by biopsy have also been observed in I-cell disease however, the characteristic secondary effect (i.e.,increased levels of lysosomal enzymes in the extracellular compartment) is only partially expressed or not expressed at all in chorionic villi, suggesting an alternative mechanism for the transport of lysosomal proteins. Although... 

Haase H, Beyersmann D (2002) Intracellular zinc distribution and transport in C6 rat glioma cells. Biochem Biophys Res Commun 296 923-928... 

Ethanol impairs monosaccharide uptake and affects the synthesis, intracellular transport, sub-cellular distribution and secretion of these glycoproteins, suggesting alterations in glycosyla-tion. Ethanol has been shown to increase the uptake of monosaccharides and the protein levels of GLUTl but decreased those of mannosidase II. It alters the carbohydrate moiety of proteins and increases cell surface glycoproteins containing terminal mannose [83]. 

The human genome contains nearly 900 genes that encode transporters, of which over 300 are intracellular transporters [1] responsible for transporting a wide range of molecules across the membrane [2]. Further classification of these transporters into families such as the solute carrier dass (SLC) [3] and ATP binding cassette (ABC) family 4, 5] is possible. Transporters play a major role in clinical pharmacology as their adequate bioavailability determines the successful oral delivery of many therapeutics. Membrane transporter proteins are associated with drug absorption (uptake), tissue distribution (efflux and uptake), metabolism (hepatic efflux and uptake), and elimination (renal, biliary transporters, and breast milk efflux and uptake) [6, 7]. 

In addition to the crucial fiinaion of centrosomes in chromosome segregation and cytokinesis, centrosomes coordinate all microtubule-related cellular functions, including cell shape, polarity, adhesion and motility, as well as the intracellular transport and positioning of organelles by controlling the number, polarity and distribution of microtubules. Thus it was interesting to see the effects of gain or loss of poly(ADP-ribosyl)ation activity in vivo. 

Binding of tocopherols and intracellular transport possible role in cellular signaling Binding of tocopherols and intracellular transport possible role in cellular signaling Binding and transport of a-tocopherol in cerebrospinal fluid Binding of a-tocopherol in plasma and possible role in tissue distribution... 

Active Transport. Maintenance of the appropriate concentrations of K" and Na" in the intra- and extracellular fluids involves active transport, ie, a process requiring energy (53). Sodium ion in the extracellular fluid (0.136—0.145 AfNa" ) diffuses passively and continuously into the intracellular fluid (<0.01 M Na" ) and must be removed. This sodium ion is pumped from the intracellular to the extracellular fluid, while K" is pumped from the extracellular (ca 0.004 M K" ) to the intracellular fluid (ca 0.14 M K" ) (53—55). The energy for these processes is provided by hydrolysis of adenosine triphosphate (ATP) and requires the enzyme Na" -K" ATPase, a membrane-bound enzyme which is widely distributed in the body. In some cells, eg, brain and kidney, 60—70 wt % of the ATP is used to maintain the required Na" -K" distribution. 

Glucose transport activity is regulated through transcriptional and translational control of the GLUT proteins, through their activity, and through alterations of their intracellular distribution. Most importantly, the GLUT4 continuously cycles between an intracellular,... 

The Ca transport ATPase of sarcoplasmic reticulum is an intrinsic membrane protein of 110 kDa [8-11] that controls the distribution of intracellular Ca by ATP-dependent translocation of Ca " ions from the cytoplasm into the lumen of the sarcoplasmic reticulum [12-16],... 

The sarcoplasmic reticulum (SR) was first identified as the major mobilizable intracellular store of Ca2+ in skeletal muscles through the work of S. Ebashi, W. Hasselbach and A. Weber (review in Ebashi 1991). Identification of the SR and its role in smooth muscle met some early difficulties, partly due to the destructive effects of osmium fixation. Eventually the SR of smooth muscle was also identified, quantitated and its spatial distribution, peripheral and central, determined (Somlyo et al 1971, Devine et al 1971). Strontium (Sr), used as an electron opaque analogue of Ca2+, permitted direct, electron microscopic visualization of divalent cation transport into the SR (Somlyo Somlyo 1971). 

The mutation of Tyr3356-68 introduces a new paradigm in the family of Na+/CIndependent transporters, i.e., mutation causing spontaneous changes in the distribution between individual functional states in the translocation cycle. Importantly, by systematic mutations of conserved intracellular residues in the hDAT, we have now identified... 

In many eukaryotic plasma membranes, PS resides in the inner leaflet (Schroit and Zwaal, 1991 Zachowski, 1993). This transbilayer distribution of membrane hpids is not a static situation but a result of balance between the inward and outward translocation of phospholipids across the membranes. Recent studies showed that the transbilayer lipid asymmetry is regulated by several lipid transporter proteins, such as aminophospholipid translocase (Daleke and Lyles, 2000), ATP-binding cassette transporter family (van Helvoort et al, 1996 Klein et al, 1999), and phospholipid scramblase (Zhou et al, 1997 Zhao et al, 1998). An increment of intracellular due to cell activation, cell injury, and apoptosis affects the activities of these transporters, resulting in exposure of PS (Koopman et al, 1994 Verhoven et al, 1995) and PE (Emoto et al, 1997) on the cell surface. 

Figure 2. The confocal microscopy results show the clustering of CD95 upon stimulation. Clustered CD95 co-localizes with ASM in the cell membrane. ASM is transported to the cell membrane most likely with intracellular storage vesicles, which fuse with the cell membrane upon CD95 stimulation. Unstimulated cells show a homogenous distribution of CD95 in the cell membrane. Cells were stimulated via CD95 for 2 min or left unstimulated, fixed, permeabilized, stained with a FlTC-labeled anti-CD95 and a Texas Red anti-ASM antibody and analyzed by confocal microscopy. The right pictures show the overlay.

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