Home About us Contact
|
Home About us Contact | ||
|
|
||
Transcellular Transport (transcellular + transport)
Selected AbstractsTranscellular transport of genistein, a soybean-derived isoflavone, across human colon carcinoma cell line (Caco-2)BIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 1 2001Masataka Oitate Abstract Genistein, a soybean-derived isoflavone, is thought to have an anticarcinogenic action, but little is known about the cellular mechanisms of its intestinal absorption. This study was designed to investigate the absorption mechanisms of genistein using human colon carcinoma cell line, Caco-2 cells. The apical-to-basolateral transcellular transport of genistein across a Caco-2 cell monolayer was significantly greater than that in the opposite direction. An uptake experiment revealed that cellular uptake of genistein by Caco-2 cells was concentrative. The transcellular transport of genistein was saturable and temperature-dependent, and was inhibited by other flavonoids such as rutin, quercetin, (+)-catechin and (,)-epicatechin. These results suggest that genistein is transported across Caco-2 cells by a carrier-mediated system, located on the apical membrane. Copyright © 2001 John Wiley & Sons, Ltd. [source] Mechanisms of transjunctional transport of NaCl and water in proximal tubules of mammalian kidneysACTA PHYSIOLOGICA, Issue 1 2002F. KIILArticle first published online: 30 APR 200 ABSTRACT Tight junctions and the intercellular space of proximal tubules are not accessible to direct measurements of fluid composition and transport rates, but morphological and functional data permit analysis of diffusion and osmosis causing transjunctional NaCl and water transport. In the S2 segment NaCl diffuses through tight junctions along a chloride gradient, but against a sodium gradient. Calculation in terms of modified Nernst,Fick diffusion equation after eliminating electrical terms shows that transport rates (300,500 pmol min,1 mm,1 tubule length) and transepithelial voltage of +2 mV are in agreement with observations. Diffusion coefficients are Dtj=1500 ,m2 s,1 in the S1 segment, and Dtj=90,100 ,m2 s,1 in the S2 segment where apical intercellular NaCl concentration is 132 mM, 1 mM below complete stop (Dtj=0 and Donnan equilibrium). Tight junctions with gap distance 6 Å are impermeable to mannitol (effective molecular radius 4 Å); reflection coefficients are ,=0.92 for NaHCO3 and ,=0.28 for NaCl, because of difference in anion size. The osmotic force is provided by a difference in effective transjunctional osmolality of 10 mOsm kg,1 in the S1 segment and 30 mOsm kg,1 in the S2 segment, where differences in transjunctional concentration contribute with 21 mOsm kg,1 for NaHCO3 and ,4 mOsm kg,1 for NaCl. Transjunctional difference of 30 mOsm kg,1 causes a volume flow of 2 nL min,1 mm,1 tubule length. Luminal mannitol concentration of 30 mM stops all volume flow and diffusive and convective transport of NaCl. In conclusion, transjunctional diffusion and osmosis along gradients generated by transcellular transport of other solutes account for all NaCl transport in proximal tubules. [source] Mechanisms of intercellular hypertonicity and isotonic fluid absorption in proximal tubules of mammalian kidneysACTA PHYSIOLOGICA, Issue 1 2002F. KIILArticle first published online: 30 APR 200 ABSTRACT The main purpose of this theoretical analysis (second of two articles) is to examine whether transjunctional diffusion of NaCl causes intercellular hypertonicity, which permits transcellular water transport across solute-impermeable lateral cell membranes until osmotic equilibration. In the S2 segment with tubular NaCl concentration 140 mM, the calculated apical intercellular NaCl concentration is c0 , 132 mM, which exceeds peritubular NaCl concentration by 12 mM or 22 mOsm kg,1. Variations in volume flow, junctional reflection coefficient (,NaCl=0.25,0.50), gap distance (g=6,8 Å), junctional depth (d=18,100 Å), intercellular diffusion coefficient (DLIS=500,1500 ,m2 s,1) and hypothetical active NaCl transport alter c0 only by a fraction of 1 mM. However, dilution and back-leakage of NaHCO3 lower apical intercellular hyperosmolality to ,18 mOsm kg,1. Water transport through solute-impermeable lateral cell membranes continues until intercellular and cellular osmolalities are equal. Transcellular and transjunctional volume flow are of similar magnitude (2 nL min,1 mm,1 tubule length) in the S2 segment. Thus, diffusion ensures isotonic absorption of NaCl. Two-thirds of NaHCO3 and other actively transported sodium salts are extruded into the last third of the exponentially widening intercellular space where the exposure time is only 0.9 s. Osmotic equilibration is dependent on aquaporins in the cell membranes. If permeability to water is low, transcellular water transport stops; tubular fluid becomes hypotonic; NaCl diffusion diminishes, but transjunctional water transport remains unaltered as long as transcellular transport of NaHCO3 and other solutes provides the osmotic force. [source] Simvastatin and lovastatin, but not pravastatin, interact with MDR1JOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 3 2002Toshiyuki Sakaeda The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, pravastatin, was compared with simvastatin and lovastatin from the viewpoint of susceptibility to interaction with or via the multidrug transporter, MDR1 (P-glycoprotein). This was carried out using the MDR1-overexpressing cell line LLC-GA5-COL150, established by transfection of MDR1 cDNA into porcine kidney epithelial LLC-PK1 cells, and [3H]digoxin, which is a well-documented substrate for MDR1. Pravastatin, at 25,100 ,M, had no effect on the transcellular transport of [3H]digoxin whereas simvastatin and lovastatin suppressed the basal-to-apical transport of [3H]digoxin and increased the apical-to-basal transport. It was suggested that recognition by MDR1 was due to the hydrophobicity. In conclusion, simvastatin and lovastatin are susceptible to interaction with or via MDR1, but pravastatin is not. This is important information when selecting the HMG-CoA reductase inhibitors for patients taking drugs that are MDR1 substrates. [source] The Effect of Ovariectomy and Estrogen on Penetrating Brain Arterioles and Blood-Brain Barrier PermeabilityMICROCIRCULATION, Issue 8 2009Marilyn J. Cipolla ABSTRACT Objective: We investigated the effect of estrogen replacement on the structure and function of penetrating brain arterioles (PA) and blood-brain barrier (BBB) permeability. Materials and Methods: Female ovariectomized Sprague-Dawley rats were replaced with estradiol (E2) and estriol (E3) (OVX + E;N=13) and compared to ovariectomized animals without replacement (OVX; N=14) and intact controls (CTL, proestrous; N=13). Passive and active diameters, percent tone, and passive distensibility of pressurized PA were compared. In addition, BBB permeability to Lucifer Yellow, a marker of transcellular transport, was compared in cerebral arteries. Results: Ovariectomy increased myogenic tone in PA, compared to CTL, that was not ameliorated by estrogen treatment. Percent tone at 75 mmHg for CTL vs. OVX and OVX + E was 44±3% vs. 51±1% and 54±3% (P<0.01 vs. CTL for both). No differences were found in passive diameters or distensibility between the groups. BBB permeability increased 500% in OVX vs. CTL animals; however, estrogen replacement restored barrier properties: flux of Lucifer Yellow for CTL, OVX, and OVX + E was (ng/mL): 3.4±1.2, 20.2±5.3 (P<0.01 vs. CTL), and 6.15±1.2 (n.s.). Conclusions: These results suggest that estrogen replacement may not be beneficial for small-vessel disease in the brain, but may limit BBB disruption and edema under conditions that cause it. [source] Comparison of ceftibuten transport across Caco-2 cells and rat jejunum mounted on modified ussing chambersBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 7 2003R.M. Menon Abstract Ceftibuten uptake into Caco-2 cells and intestinal brush border membrane vesicles is mediated by the dipeptide transport system (PEPT1). The apical to basolateral transport characteristics of ceftibuten across Caco-2 cells and rat jejunum mounted on a modified Ussing chamber was examined. Mannitol was used as a paracellular marker along with trans-epithelial electrical resistance (TEER) for monitoring tight junction permeability. Transport across Caco-2 cells and rat jejunum mounted on a modified Ussing chamber was linear across the concentration range 0.25,10 mm. The net flux of mannitol and ceftibuten was higher across rat jejunum compared with Caco-2 cells. At a donor concentration of 0.25 mm, ceftibuten transport across Caco-2 cells was found to be pH dependent. Glycyl proline, a dipeptide, and 2,4- dinitrophenol, an energy poison, caused a reduction in the permeability of 0.25 mm ceftibuten across Caco-2 cells. Benzoic acid and adipic acid also inhibited transcellular transport of ceftibuten. At a donor concentration of 0.25 mm, passive paracellular transport accounts for about 60% and the active carrier mediated mechanism accounts for about 40% of ceftibuten transport across Caco-2 cells. None of the inhibitors however, had a significant effect on ceftibuten transport across rat jejunum mounted on a modified Ussing chamber at a donor concentration of 0.25 mm. In the concentration range 0.25,10 mm, ceftibuten is predominantly transported by paracellular mechanisms across rat jejunum and a mixture of active and passive transport across Caco-2 cells. Copyright © 2003 John Wiley & Sons, Ltd. [source] MDR1-P-Glycoprotein (ABCB1) Mediates Transport of Alzheimer's Amyloid-, Peptides,Implications for the Mechanisms of A, Clearance at the Blood,Brain BarrierBRAIN PATHOLOGY, Issue 4 2007Diana Kuhnke Amyloid-, (A,) is the major component of the insoluble amyloid plaques that accumulate intracerebrally in patients with Alzheimer's disease (AD). It has been suggested that MDR1-P-glycoprotein (ABCB1, P-gp) plays a substantial role in the elimination of A, from the brain. In the present study, MDR1 -transfected LLC cells growing in a polarized cell layer were used to characterize the interaction of A,1-40/1-42 with P-gp. In this system, P-gp-mediated transport can be followed by the efflux of the fluorescent dye rhodamine-123, or of A, itself from the cells into the apical extracellular space. A, significantly decreased the apical efflux of rhodamine-123, and the transcellular transport of A,1-40 and A,1-42 into the apical chamber could be demonstrated using both ELISA and fluorescence (FITC)-labeled peptides. This transport was inhibited by a P-gp modulator. Furthermore, ATP-dependent, P-gp-mediated transport of the fluorescence-labeled peptides could be demonstrated in isolated, inside-out membrane vesicles. Our data support the concept that P-gp is important for the clearance of A, from brain, and thus may represent a target protein for the prevention and/or treatment of neurodegenerative disorders such as AD. [source] | ||||||||||