Polarity transport

R. Agu, H. V. Dang, M. Jorissen, T. Willems, S. Vandoninck, J. Van Lint, J. V. Vandenheede, R. Kinqet, and N. Verbeke. In vitro polarized transport of L-phenylalanine in human nasal epithelium and partial characterization of the amino acid transporters involved. Pharm Res 20 1125-1132 (2003). 

The blood-brain barrier forms the interface between the bloodstream and the brain parenchyma and thus controls the passage of endogenous substances and xenobiotics into and out of the central nervous system. Brain microvessels exhibit a variety of unique structural features, such as an extremely tight endothelium without fenestration, a very low rate of pinocytosis, tight junctions between endothelial cells excluding paracellular permeability, and a series of polarized transport proteins. The following chapter describes the structural and functional characteristics of the blood-brain barrier with emphasis on transport proteins, as well as in vitro techniques, which allow studying this complex barrier in the brain. 

Wils, P., Phung-Ba, V., Warnery, A., et al. (1994) Polarized transport of docetaxel and vinblastine mediated by P-glycoprotein in human intestinal epithelial cell monolayers. Biochem. Pharmacol. 48, 1528-1530. 

G.A.Prinz, Spin-Polarized Transport, Phys. Today 48 (1995) 58. 

Tries and Kuebler [18] indicated a total surface area of 350 square meters and a mass of 100 g. 4Simionescu et al. [19] defined transcytosis as the polarized transport of plasma proteins across cells via caveolae or endosomal transport vesicles to the subjacent tissue or bidirectionally across other polarized cells such as epithelial cells. 

An equivalent circuit of resonant-tunneling nanostructures taking into account spin-polarized transport of charge carriers is proposed. It is based on the approximation of I-V characteristics and represents spin shifted energy levels in the quantum well. 

Adventitious shoot formation occurred when the roots were cultured onto auxin-free medium as mentioned above. Since the decrease of auxin levels seemed to be important for the adventitious shoot formation, the influences of auxin inhibitors on shoot formation on the cultured root segments were investigated. The auxin polar transport inhibitor, 2,3,... 

Polar transport of endogenous lAA was indispensable for the adventitious shoot formation on the cultured roots of ipecac. This micropropagation system can be easily applied to other woody species if detailed mechanism will be elucidated. 

Schmidt, G. and L.W. Molenkamp, Electrical Spin Injection Spin-Polarized Transport from Magnetic into Non-Magnetic Semiconductors, in Semiconductor Spintronics and Quantum Computation, D.D. Awschalom, D. Loss, and N. Samarth, Editors. 2002, Springer Berlin, p. 93-106. 

Chung SM, Park EJ, Swanson SM, Wu TC, and Chiou WL. Profound Effect of Plasma Protein Binding on the Polarized Transport of Furosemide and Verapamil in the Caco-2 Model. Pharm Res 2001 18 544-547. 

The data show that metabolism of both jasmonic acid and hydrojasmonic acid is predominantly by hydroxyylation with subsequent glucosylation. It is still unknowm whether this metabolism leads to inactivation of these phsyiologically high potent molecules and/or to more polar transport forms. 

The first study relates to the identification and design of novel herbicides and plant growth regulators that act by inhibiting polar transport of the plant hormone auxin (100). Previous studies (101) had identified seven auxin transport inhibitors, from which it was possible to describe a three-component... 

Primary trophoblast cells (and ahso most cell lines of tro-phoblast origin) do not grew into confluent monolayers in culture (Cariappa et ai, 2003). This inhibits studies on polarized transport of nutrients and other compounds. They are difficult to culture because of contamination by other cell types and poor viability (Choy et ai, 2000). Villous and extravillous cytotrophoblasts differ in their function and characteristics. As studied by immunofluorescence, Ockleford and coworkers (2004) have shown a much higher cytokeratin expression in extravillous cytotrophoblasts compared to villous cytotrophoblasts,... 

Figure 3.11 Hydrogen pressure drops due to depletion, concentration polarization, transport in the palladium membrane and porous support compared to the total hydrogen partial pressure drop. (Source Reproduced from Ref [31])...

The polar transport of auxin in early globular embryos is essential for the establishment of bilateral symmetry during plant embryogenesis. Interference with this transport causes a failure in the transition from axial to bilateral symmetry and results in the formation of embryos with fused cotyledons (Liu et at, 1993). 

Jonsson, H., Heisler, M.G., Shapiro, B.E., Mjolsness, E., Meyerowitz, E.M. (2006). An auxin-driven polarized transport model for phyllotaxis. Proceedings of the National Academy of Sciences USA, Vol.103, pp. 1633-1638. 

Mitchison, G.J. (1981). The polar transport of auxin and vein patterns in plants. Philosophical Transactions of the Royal Society, London, series B, Vol. 5, pp. 461-471. 

There seems to be no polar or local distribution of lAA after lAA application [32]. The localized effect of the response may thus not come from actual polar transport in the large coenocytic cell. Altogether this system is not yet confirmed definitely to be hormonally regulated. 

NPA and other synthetic auxin transport inhibitors can block PAT when they are incorporated into the receiver blocks in a classical donor-to-receiver polar transport assay. Figure 4 shows that quercetin in receiver blocks can inhibit lAA arrival, but only for the first 2 h of the transport test. Thereafter, the radioactivity delivered to the receiver blocks is increased compared to controls. In some experiments lAA (or NAA) arrival in quercetin-containing receiver blocks is increased at earlier times. A crossover is never observed when NPA is used. Quercetin and other flavonoids bind strongly to cellulose [31 ] and, unlike NPA, do not diffuse away... 

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