Colon transporter

Feldman GM Department of Veterans Affairs, Medical Center Richmond, Virginia Colonic transport of bicarbonate, ammonium small organic anions Department of Veterans Affairs, Research and Development,... 

Jack Products, a U.S. Class 1 railroad and North America s leading independent intermodal terminal operator, respectively, have invested 60 million for start-up expenses to revive and modernize the 143-year old first transcontinental railroad of the Americas. Fnlly operational in 2000, the revitalized railroad provides an efficient intermodal link for world commerce and complements the existing transportation provided by the canal, the Colon Free Trade Zone, and the port terminals. 

ENaC is located in the apical membrane of polarized epithelial cells where it mediates Na+ transport across tight epithelia [3], The most important tight epithelia expressing ENaC include the distal nephron of the kidney, the respiratory epithelium, and the distal colon. The basic function of ENaC in polarized epithelial cells is to allow vectorial transcellular transport of Na+ ions. This transepithelial Na+ transport through a cell involves... 

Facilita GLUT1 ive bidirectionai transporters Brain, kidney, colon, placenta, erythrocyte Uptake of glucose... 

OITATE M, NAKAKI R, KOYABU N, TAKANAGA H, MATSUO H, OHTANI H, SAWADA Y (2001) TranSCellular transport of genistein, a soybean-derived isoflavone, across human colon carcinoma cell line (Caco-2). Biopharm Drug Dispos. 22 23-9. 

The transport number is a measure of the permselectivity of a membrane. If, for example, a membrane is devoid of colons, then all current through the membrane is carried by the counterion, and the transport number = 1. The transport numbers for the membrane and the solution are different in practical ED applications. 

H. Liu, A. T. Trieu, L. A. Blaylock, and M. J. Harrison, Cloning and characterization of two phosphate transporters from Medicago truncatula roots Regulation in response to phosphate and to colonization by arbuscular mycorrhizal fungi. Mol. Plant-Microbe Interact. 11 A (1998). 

V. cholerae is a gram-negative bacillus. Vibrios pass through the stomach to colonize the upper small intestine. Vibrios have filamentous protein extensions that attach to receptors on the intestinal mucosa, and their motility assists with penetration of the mucus layer.2 The cholera enterotoxin consists of two subunits, one of which (subunit A) is transported into the cells and causes an increase in cyclic AMP, which leads to a deluge of fluid into the small intestine.20 This large volume of fluid results in the watery diarrhea that is characteristic of cholera. The stools are an electrolyte-rich isotonic fluid, the loss of which results in blood volume depletion followed by low blood pressure and shock.2 Of note, the diarrheal fluid is highly infectious. 

Tanaka, Y. Taki, Y. Sakane, T. Nadai, T. Sezaki, H. Yamashita, S., Characterization of drug transport through tight-junctional pathway in Caco-2 monolayer Comparison with isolated rat jejunum and colon, Pharm. Res. 12, 523-528 (1995). 

Another way to increase the entry of Ca2+ across the plasma membrane is to hyperpolarize the plasma membrane by elevating active ion transport. Fischer et al. [130] demonstrated that hyperpolarization of colonic epithelial cells (HT-29) with carbachol elevates the intracellular levels of Ca2+, [Ca2+]i while depolarization with gramicidin D or elevation of K+ in the bathing fluid reverses it. Treatment with 0.1 mM carbachol produced a spontaneous increase in [Ca2+]i from 63 nM to 901 nM. This lasted for about 3 min, beyond which a plateau level of 309 nM was maintained. While the initial Ca2+ transient was present in Ca2+-free medium containing 0.1 mM EGTA, the plateau phase was suppressed to baseline levels, suggesting that carbachol initially releases Ca2+ from the intracellular stores and subsequently increases the Ca2+ entry across the plasma membrane. In cells hyperpolarized with carbachol, induction of depolarization by ele-... 

Another human colonic cancer cell line is T84 this develops monolayers of high TER ( 1000 Q cm2) when grown on permeable supports, but cells are not well differentiated and have been described as resembling a colonic crypt cell phenotype. Hence, these cells have been used mainly in studies of epithelial ion transport and are generally not considered to be adequate for drug transport studies, particularly with respect to carrier-mediated processes [10, 79, 82-84]. 

Another limitation of the Caco-2 monolayers is their colonic origin and tight paracellular pathway, which tend to lead to underestimations in permeability to paracellularly transported compounds [97]. This is likely to be correct for small compounds (MW < 150) - i.e., compounds smaller than normal drugs - but it remains to be seen to what extent the Caco-2 model gives false-negative predictions of the fraction absorbed for polar drugs of normal size in humans where para-... 

The paracellular pathway, between the epithelial cells, is both size- (MW, volume) and charge-dependent [60, 109, 110]. In general, compounds that are limited to paracellular transport are not efficiently absorbed due to the small available absorptive area and the restriction by tight junctions. The molecular weight cut-off seems to be around 400 g mol-1 and 300 g mol-1 for the small and large intestine respectively, and 300 g mol-1 for the Caco-2 cell monolayers [60], which shows the more colonic nature of the Caco-2 monolayer model. Compounds with a... 

Berteloot, A., Common characteristics for Na1 -dependent sugar transport in Caco-2 cells and human fetal colon, J. Membr. Biol 1987, 99, 113-125. 

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