Cells polarization

The polarization cell is an electrochemical component in which nickel or stainless steel electrodes are immersed in 50% KOH solution [9]. With ac, the... 

The polarization cell must be inspected at regular intervals (e.g., twice a year) to check water loss caused by electrolysis. If necessary, the correct level must be restored with deionized water. In addition, the electrolyte should be renewed every 4 years. It is recommended that the dc decoupling device be designed so that the maximum expected failure current flows through the smallest possible polarization cell in order to load the cathodic protection as little as possible. 

Fig. 14-7 Circuit diagram for a dc decoupling device with polarization cell. (KE) insulated cable end sealing, (E) grounding installation, (1) grounding side bar, (2) polarization cell, (3) disconnecting shackle.

Polarization cells and diode voltage arresters can be used for this purpose. 23.5.4.2.1 Polarization Cells... 

The construction and action of polarization cells are described in Section 14.2.2.4. Difficulties in measuring off potentials can occur when polarization cells are connected in the circuit. The voltage of the polarization cell is the difference... 

Fig. 23-13 Difference in off potentials with and without connected polarization cells (P = location of polarization cells).

Pol-klemme, /. Elec.) pole terminal, pole clamp, -kdrper, m., -kdrperchen, n. Biol.) polar body, polar cell. 

Lizlovs, E. A., Polarization Cell for Potentiostatic Crevice Corrosion Testing , J. Electro-chem., Soc., 117, 256C, Atlantic City Meeting (1970)... 

Nelson, W.J. Veshnock, P.J. (1987). Ankyrin binding to (Na + K )-ATPase and implications for the organization of membrane domains in polarized cells. Nature 328, 533-536. 

In culture, the human colon carcinoma cell hne Caco-2 spontaneously differentiates at confluency into polarized cells with enterocyte-like characteristics. The principle of this approach consists of following the passage of the compound of interest from the apical or lumen-like sides to the basolateral or lymph-hke sides of Caco-2 cells, thus following the absorption of the compound per se. One obhgate step for fat-soluble nutrients such as carotenoids to cross the intestinal barrier is their incorporation into CMs assembled in the enterocytes. Under normal cell culture conditions, Caco-2 cells are unable to form CMs. When supplemented with taurocholate and oleic acid, Caco-2 cells were reported to assemble and secrete CMs. ... 

In previous reviews on this matter by Gogelein [9] and myself [10] it has been pointed out that the Cl -channels of the central nervous system and of skeletal muscle are distinct from those of non-excitable cells. The latter entity is in itself obviously heterogeneous with respect to its occurrence and function. In apolar as well as in polarized cells Cl -channels may be involved in volume regulation. As a simple rule gating of K" - and Cl -channels is likely to occur whenever cell volume has to be down-regulated [11], as is the case in regulatory volume decrease of cell volume. A simple means to induce this phenomena is the exposure of cells to hypoosmolar solutions [12]. For example Cl -channels play an important role in... 

While both paracellular and passive transcellular pathways are available to a solute, the relative contribution of each to the observed transport will depend on the properties of the solute and the membrane in question. Generally, polar membrane-impermeant molecules diffuse through the paracellular route, which is dominated by tight junctions (Section III.A). Exceptions include molecules that are actively transported across one or both membrane domains of a polarized cell (Fig. 2). The tight junction provides a rate-limiting barrier for many ions, small molecules, and macromolecules depending on the shape, size, and charge of the solute and the selectivity and dimensions of the pathway. 

At a more molecular level, the influences of the composition of the membrane domains, which are characteristic of a polarized cell, on diffusion are not specifically defined. These compositional effects include the differential distribution of molecular charges in the membrane domains and between the leaflets of the membrane lipid bilayer (Fig. 3). The membrane domains often have physical differences in surface area, especially in the surface area that is accessible for participation in transport. For example, the surface area in some cells is increased by the presence of membrane folds such as microvilli (see Figs. 2 and 6). The membrane domains also have differences in metabolic selectivity and capacity as well as in active transport due to the asymmetrical distribution of receptors and transporters. 

The Caco-2 cell line was isolated from a human colon carcinoma, and has been characterized as one of the best in vitro models of intestinal epithelium. Indeed, in contrast to other intestinal cell lines, Caco-2 cells are able to constitute a homogenous monolayer and to spontaneously differentiate into polarized cells, highly similar to human mature enterocytes, after approximately 2 weeks of culture. Furthermore, the Caco-2 cells present microvillosities at the apical side and have a high transmembrane resistivity, which confirms the fact that the cells are confluent and link to one another via gap junctions. Finally, they can absorb different compounds, express many enzymes involved in intestinal metabolic pathways (Pinto et al. 1983, Musto et al. 1995, Salvini et al. 2002), and give reproducible in vitro results consistent with results obtained in in vivo studies (Artursson and Karlsson 1991). 

E. G., Creation of polarized cells coexpressing CYP3A4, NADPH cytochrome P450 reductase and MDRl/P-glycoprotein, Pharm. Res. 2000, 37, 803-810. 

The presence of a transporter can be assessed by comparing basolateral-to-apical with apical-to-basolateral transport of substrates in polarized cell monolayers. If P-gp is present, then basolateral-to-apical transport is enhanced and apical-to baso-lateral transport is reduced. Transport experiments are in general performed with radioactively labeled compounds. Several studies have been performed with Caco-2 cell lines (e.g. Ref. [85]). Since Caco-2 cells express a number of different transporters, the effects measured are most probably specific for the ensemble of transporters rather than for P-gp alone. P-gp-specific transport has been assayed across confluent cell layers formed by polarized kidney epithelial cells transfected with the MDR1 gene [86], Figure 20.11 shows experimental data obtained with these cell lines. A rank order for transport called substrate quality was determined for a number of compounds [86]. The substrate quality is a qualitative estimate, but nevertheless allows an investigation of the role of the air/water (or lipid/water) partition coefficient, log Kaw, for transport as seen in Fig. 20.11(A). For most of the compounds, a linear correlation is observed between substrate quality and log Kaw- However, four compounds are not transported at all despite their distinct lipophilicity. A plot of the substrate quality as a function of the potential of a... 

Fig. 20.11. Substrate quality obtained by comparing basolateral-to-apical with apical-to-basolateral transport of substrates in polarized cell monolayers of MDR1-transfected cell lines [86] plotted versus (A) the log of the air/water partition coefficient, or (B) H-bond energy (arbitrary units, EUh cf. text). Units of the air/ water partition coefficient were [M ]. Compound (concentrations in Ref. [86] in brackets) were clozapine (50 nM) (1) cyclosporin A (2 tM) (2) daunorubicin (3) dexamethasone (2 tM) (4) digoxin (2 pM) (5) domperidone (2 pM) (6) etoposide (7) flunitrazepam (500 nM) (8) haloperidol (50 nM) (9) ivermectin (50 nM) (10) loperamide (2 pM) (11) morphine (2 pM) (12) ondansetron...

Ligand-receptor complexes that do not dissociate in the EEs have different fates. In some cells, they may be returned to the same plasma membrane compartment from which they originated, whereas in polarized cells such as endothelial cells or astrocytes they can be moved to a different plasma membrane domain, resulting in transcytosis. In other cases, the complexes go to LEs and lysosomes for degradation. In neurons, these vesicles may serve as signaling organelles that are transported from the EEs back to the cell body where they influence gene expression [71]. 

These include the variations of sacrificial anode, sonication, and alternating polarity cell mentioned above, different solvent/co-solvent and electrolyte systems, monomer concentration, total current passed, and temperature. Best results appear to be obtained with THF and dimethyl ether (DME) as solvent and a perchlorate supporting electrolyte in some systems using fluorides, electrolyte decomposition occurred releasing fluoride anion which formed unreactive fluorosilanes.125... 

The GPI-anchored proteins are related to various cellular functions. For example, they participate in the protein sorting to the apical surface of polarized cells and clathrin-independent endocytosis (see Section III,... 

Eaton, S., and Simons, K. (1995). Apical, basal, and lateral cues for epithelial polarization. Cell. 82, 5-8. 

MDCK Dog kidney epithelial cells Polarized cells with low intrinsic expression of transporters Suitable cell fine for transfections... 

MDCK Madin-Darby canine kidney (MDCK) cells have received attention as an alternative to Caco-2 cells for permeability measurements. When grown under standard culture conditions, MDCK cells develop tight junctions and form monolayers of polarized cells. The main advantage over Caco-2 cells is the shorter culture time to confluence (3-5 days). The transep-ithelial electrical resistance of MDCK cells is lower than that of Caco-2 cells and thus, closer to the TEER of the small intestine in vivo. The permeability coefficients of hydrophilic compounds are usually lower in Caco-2 cells than in MDCK cells, which is consistent with the lower TEER values for MDCK cell monolayers. The nonhuman (canine) and nonintestinal (renal) origin of MDCK cells is considered as a disadvantage. They have low expression levels of transporter proteins and low metabolic activity [34], MDCK cells that are stably transfected with P-gp/MDRl are often proposed as an alternative for Caco-2 cells to study bidirectional transport of compounds and, more... 

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