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Basolateral Membrane (basolateral + membrane)
Selected AbstractsFibroblast growth factor 23 reduces expression of type IIa Na+/Pi co-transporter by signaling through a receptor functionally distinct from the known FGFRs in opossum kidney cellsGENES TO CELLS, Issue 5 2005Xiaomei Yan Fibroblast growth factor (FGF) 23 is an important phosphaturic factor that inhibits inorganic phosphate (Pi) reabsorption from the renal proximal tubule. Its overproduction and proteolysis-resistant mutation such as R179Q cause tumor-induced osteomalacia and autosomal dominant hypophosphatemic rickets, respectively. To clarify the signaling mechanisms of FGF23 that mediate the reduction of Pi reabsorption, we inhibited the function of the known FGFRs in opossum kidney (OK-E) cells by expressing a dominant-negative (DN) form of FGFR. OK-E cells, which represent the renal proximal tubular cells, expressed all four known FGFRs. FGF23(R179Q) bound to and activated FGFR2, a prominent FGFR expressed in OK-E cells. The activated receptor transmitted a signal to increase the expression of type IIa Na+/Pi co-transporter and the Pi uptake. Expression of FGFR2(DN), which suppresses the major FGFR-mediated signal through the FRS2,-ERK pathway, reversed the function of FGF23(R179Q). When FGF23(R179Q) was applied to the basolateral side of polarized OK-E cells, regardless of the FGFR2(DN) expression, the apical Pi uptake decreased significantly. The apical application of FGF23(R179Q) in the polarized cells did not show such decrease but increase. The exogenously expressed FGFR2 was detectable only at the apical membrane. These results suggest that an FGF23 receptor, which is functionally distinct from the known FGFRs, is expressed at the basolateral membrane of OK-E cells. [source] Expression of an Aedes aegypti cation-chloride cotransporter and its Drosophila homologuesINSECT MOLECULAR BIOLOGY, Issue 4 2003V. Filippov Abstract Insects maintain haemolymph homeostasis under different environmental conditions by modulating the concentrations of Na+, K+ and Cl, ions. One group of proteins involved in ion transport across cell membranes consists of cation-chloride cotransporters that form a family of structurally similar proteins. Although much is known about these proteins in mammalian systems, our understanding of them in insects is lacking. The recent sequencing of two insect genomes, Drosophila and Anopheles, enabled us to identify globally members of the family of cation chloride cotransporters in these insects. Using RT-PCR we monitored the transcription of members of this family in development and in several tissues. Our analyses showed that transcription of these genes differ considerably from the ubiquitously and highly expressed CG5594 gene to the almost silent gene CG31547. Comparison of Drosophila CG12773 and its Aedes homologue AaeCG12773 showed that they have similar transcript expression profiles. Immunohistochemical analysis of AaeCG1277 gene expression revealed that it is highly expressed in the gut of larvae and female adults but not in Malpighian tubules. A more detailed analysis showed that this protein is localized predominantly in the basolateral membrane of these tissues. This expression pattern confirmed the results of RT-PCR analysis. We also created a mutant for one of the genes, CG10413, in Drosophila using P-element excision. Analysis of this mutant showed this protein does not appear to be essential for development. [source] OCTN3: A Na+ -independent L -carnitine transporter in enterocytes basolateral membraneJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2005J.M. Durán L -carnitine transport has been measured in enterocytes and basolateral membrane vesicles (BLMV) isolated from chicken intestinal epithelia. In the nominally Na+ -free conditions chicken enterocytes take up L -carnitine until the cell to medium L -carnitine ratio is 1. This uptake was inhibited by L -carnitine, D -carnitine, ,-butyrobetaine, acetylcarnitine, tetraethylammonium (TEA), and betaine. L - 3H-carnitine uptake into BLMV showed no overshoot, and it was (i) Na+ -independent, (ii) trans-stimulated by intravesicular L -carnitine, and (iii) cis-inhibited by TEA and cold L -carnitine. L - 3H-carnitine efflux from L - 3H-carnitine preloaded enterocytes was also Na+ -independent, and trans-stimulated by L -carnitine, D -carnitine, ,-butyrobetaine, acetylcarnitine, TEA, and betaine. Both, uptake and efflux of L -carnitine were inhibited by verapamil and unaffected by either extracellular pH or palmitoyl- L -carnitine. RT-PCR with specific primers for the mouse OCTN3 transporter revealed the existence of OCTN3 mRNA in mouse intestine, which was confirmed by in situ hybridization studies. Immunohystochemical analysis showed that OCTN3 protein was mainly associated with the basolateral membrane of rat and chicken enterocytes, whereas OCTN2 was detected at the apical membrane. In conclusion, the results demonstrate for the first time that (i) mammalian small intestine expresses OCTN3 mRNA along the villus and (ii) that OCTN3 protein is located in the basolateral membrane. They also suggest that OCTN3 could mediate the passive, Na+ and pH-independent L -carnitine transport activity measured in the three experimental conditions. © 2004 Wiley-Liss, Inc. [source] ASSESSING ABSORBABILITY OF BIOACTIVE COMPONENTS IN ALOE USING IN VITRO DIGESTION MODEL WITH HUMAN INTESTINAL CELLJOURNAL OF FOOD BIOCHEMISTRY, Issue 2 2010SOON-MI SHIM ABSTRACT This study used a simulated in vitro digestion model coupled with caco-2 cell to assess the digestive stability and absorption of aloin, aloe-emodin and aloenin A. Aloenin A and aloe-emodin were stable and entirely recovered during simulated digestion, but 50% of aloin was lost. Approximately 53.2, 7.3 and 28.7% of aloe-emodin, aloenin A and aloin, respectively, was transported into both apical and basolateral compartments after 1 h incubation in caco-2 cell. The involvement of several transporter proteins for aloin and aloenin A was examined. An inhibitor of SGLT1 on apical surface (phloridzin) or that of GLUT2 on basolateral membrane (cytochalasin B) reduced the absorption of aloin by 40 or 60%, respectively, indicating that aloin is likely to be a partial substrate of SGLT1. In the presence of an efflux transporter inhibitor (verapamil), the transport of aloenin A through an intentinal apical membrane increased up to 2.1 times compared with the control (without verapamil). PRACTICAL APPLICATIONS Our results on both digestive stability and intestinal absorption characteristics of bioactive components in aloe could be of helpful information for promoting its bioavailability. The in vitro technique described in this study provides a rapid and cost-effective alternative for predicting bioavailability of biomarkers in aloe functional food. [source] Localization of organic cation/carnitine transporter (OCTN2) in cells forming the blood,brain barrierJOURNAL OF NEUROCHEMISTRY, Issue 1 2008Dorota Miecz Abstract Carnitine ,-hydroxy-,-(trimethylammonio)butyrate , a compound necessary in the peripheral tissues for a transfer of fatty acids for their oxidation within the cell, accumulates in the brain despite low ,-oxidation in this organ. In order to enter the brain, carnitine has to cross the blood,brain barrier formed by capillary endothelial cells which are in close interaction with astrocytes. Previous studies, demonstrating expression of mRNA coding two carnitine transporters , organic cation/carnitine transporter 2 (OCTN2) and B0,+ in endothelial cells, did not give any information on carnitine transporters polarity in endothelium. Therefore more detailed experiments were performed on expression and localization of a high affinity carnitine transporter OCTN2 in an in vitro model of the blood,brain barrier by real-time PCR, western blot analysis, and immunocytochemistry. The amount of mRNA was comparable in endothelial cells and kidney, when referred to house-keeping genes, it was, however, significantly lower in astrocytes. Polarity of OCTN2 localization was further studied in an in vitro model of the blood,brain barrier with use of anti-OCTN2 antibodies. Z -axis analysis of the confocal microscope pictures of endothelial cells, with anti-P-glycoprotein antibodies as the marker of apical membrane, showed OCTN2 localization at the basolateral membrane and in the cytoplasmic region in the vicinity of nuclei. Localization of OCTN2 suggest that carnitine can be also transported from the brain, playing an important role in removal of certain acyl esters. [source] Molecular Diversity of Vasotocin-Dependent Aquaporins Closely Associated with Water Adaptation Strategy in Anuran AmphibiansJOURNAL OF NEUROENDOCRINOLOGY, Issue 5 2010M. Suzuki Anuran amphibians represent the first vertebrates that adapted to terrestrial environments, and are successfully distributed around the world, even to forests and arid deserts. Many adult anurans have specialised osmoregulatory organs, in addition to the kidney (i.e. the ventral pelvic skin to absorb water from the external environments and a urinary bladder that stores water and reabsorbs it in times of need). Aquaporin (AQP), a water channel protein, plays a fundamental role in these water absorption/reabsorption processes. The anuran AQP family consists of at least AQP0-AQP5, AQP7-AQP10 and two anuran-specific types, designated as AQPa1 and AQPa2. For the three osmoregulatory organs, AQP3 is constitutively located in the basolateral membrane of the tight-junctioned epithelial cells, allowing water transport between the cytoplasm of these cells and the neighbouring tissue fluid at all times. On the other hand, AQPs at the apical side of the tight epithelial cells are different among these organs, and are named kidney-type AQP2, ventral pelvic skin-type AQPa2 and urinary bladder-type AQPa2. All of them show translocation from the cytoplasmic pool to the apical plasma membrane in response to arginine vasotocin, thereby regulating water transport independently in each osmoregulatory organ. It was further revealed that, in terrestrial and arboreal anurans, the bladder-type AQPa2 is expressed in the pelvic skin, together with the pelvic skin-type AQPa2, potentially facilitating water absorption from the pelvic skin. By contrast, Xenopus has lost the ability to efficiently produce pelvic skin-type AQPa2 (AQP-x3) because Cys-273 of AQP-x3 and/or Cys-273-coding region of AQPx3 mRNA attenuate gene expression at a post-transcriptional step, presumably leading to the prevention of excessive water influx in this aquatic species. Collectively, the acquisition of two forms of AQPa2 and the diversified regulation of their gene expression appears to provide the necessary mechanisms for the evolutionary adaptation of anurans to a wide variety of ecological environments. [source] Transport of Peptidomimetic Drugs by the Intestinal Di/tri-peptide Transporter, PepT1BASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 6 2002Birger Brodin The physiological function of the system is to transport small peptides resulting from digestion of dietary protein. Moreover, due to the broad substrate specificity of the system, it is also capable of transporting a number of orally administered peptidomimetic drugs. Absorbed peptides may be hydrolysed in the cells due to the high peptidase activity present in the cytosol. Peptidomimetic drugs may, if resistant to the cellular enzyme activity, pass the basolateral membrane via a basolateral peptide transport mechanism and enter the systemic circulation. As the number of new peptide and peptidomimetic drugs are rapidly increasing, the peptide transport system has gained increasing attention as a possible drug delivery system for small peptides and peptide-like compounds. In this paper we give an updated introduction to the transport system and discuss the substrate characteristics of the di/tri-peptide transporter system with special emphasis on chemically modified substrates and prodrugs. [source] Purinergic regulation of the epithelial Na+ channelCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2009Lauren M O'Mullane Summary 1. The epithelial Na+ channel (ENaC) is a major conductive pathway that transports Na+ across the apical membrane of the distal nephron, the respiratory tract, the distal colon and the ducts of exocrine glands. The ENaC is regulated by hormonal and humoral factors, including extracellular nucleotides that are available from the epithelial cells themselves. 2. Extracellular nucleotides, via the P2Y2 receptors (P2Y2Rs) at the basolateral and apical membrane of the epithelia, trigger signalling systems that inhibit the activity of the ENaC and activate Ca2+ -dependent Cl, secretion. 3. Recent data from our laboratory suggest that stimulation of the P2Y2Rs at the basolateral membrane inhibits ENaC activity by a signalling mechanism that involves G,, subunits freed from a pertussis toxin (PTX)-sensitive G-protein and phospholipase C (PLC) ,4. A similar signalling mechanism is also partially responsible for inhibition of the ENaC during activation of apical P2Y2Rs. 4. Stimulation of apical P2Y2Rs also activates an additional signalling mechanism that inhibits the ENaC and involves the activated G, subunit of a PTX-insensitive G-protein and activation of an unidentified PLC. The effect of this PTX-insensitive system requires the activity of the basolateral Na+/K+/2Cl, cotransporter. [source] DIFFERENTIAL REGULATION OF ANGIOTENSIN II RECEPTORS DURING RENAL INJURY AND COMPENSATORY HYPERTROPHY IN THE RATCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2005Emma Joly SUMMARY 1.,The renin-angiotensin system may be involved in the compensatory adaptations occurring after the reduction of renal mass and during the consecutive changes leading to chronic renal failure. We therefore investigated the regulation of angiotensin II receptors in two models of renal hypertrophy in the rat: hypertrophy following uninephrectomy (UNx) or subtotal nephrectomy (STNx). The level of angiotensin type 1 (AT1A -R and AT1B -R) and type 2 (AT2 -R) receptor mRNA was quantified by competitive reverse transcription-polymerase chain reaction (RT-PCR) in specific renal zones and the intrarenal distribution of angiotensin II receptors was analysed by immunohistochemistry. 2.,In the UNx rats, AT1 -R mRNA expression was not modified in the cortex or in the inner stripe of the outer medulla of the residual kidney at any time after the surgery (1, 4 and 12 weeks). In contrast, AT1 -R mRNA expression was significantly reduced in these zones in STNx rats (,33% and ,40%, respectively). This downregulation was organ-specific, as AT1 -R mRNA levels were not modified in the liver. The proportions of AT1 -R subtype (AT1A and AT1B) mRNA were unchanged by UNx or STNx. Very low levels of AT2 -R mRNA were found in the cortex of all groups. Immunostaining revealed a similar localization of AT1 -R in mesangial cells, proximal tubule, basolateral membrane of thick ascending limb, in both models of hypertrophy. AT1 -R labelling was also detected in the apical membrane of intercalated cells of cortical collecting ducts. 3.,This differential mRNA expression of angiotensin II receptors during compensatory hypertrophy and renal injury suggests that the development of renal hypertrophy is independent of AT1 -R and AT2 -R gene expression levels. [source] Dietary pectin up-regulates monocaboxylate transporter 1 in the rat gastrointestinal tractEXPERIMENTAL PHYSIOLOGY, Issue 4 2009Doaa Kirat This work was undertaken to study the effect of pectin feeding on the expression level, cellular localization and functional activity of monocarboxylate transporter 1 (MCT1) in the gastrointestinal tract of rats. The results indicated that MCT1 protein level was significantly increased along the entire length of the gastrointestinal tract of pectin-fed rats in comparison with control animals. Immunohistochemical analysis revealed an increase in MCT1 in the stratified squamous epithelia of the forestomach as well as in the basolateral membranes of the cells lining the gastric pit of the glandular stomach of pectin-fed rats when compared with control animals. The parietal cells, which showed barely any or no detectable MCT1 in the control group, exhibited a strong intensity of MCT1 on the basolateral membranes in pectin-fed rats. In the small intestine of pectin-fed rats, strong immunopositivity for MCT1 was detected in the brush border and basolateral membranes of the absorptive enterocytes lining the entire villi, while in control rats, weak reactivity was detected on the brush border membrane in a few absorptive enterocytes in the villus tip. In the large intestine of control animals, MCT1 was detected on the basolateral membranes of the epithelia lining the caecum and colon. This staining intensity was markedly increased in pectin-fed rats, along with the appearance of strong reactivity for MCT1 on the apical membranes of the surface and crypt epithelia of caecum and colon. Our results also showed that MCT1 co-localizes with its chaperone, basigin (CD147), in the rat gastrointestinal tract, and that the pectin feeding increased the expression of CD147. In vivo functional studies revealed an enhanced acetate absorption in the colon of pectin-fed in comparison with control animals. We conclude that MCT1 is up-regulated along the gastrointestinal tract of pectin-fed rats, which might represent an adaptive response to the increased availability of its substrates. [source] Chromium nanoparticle exhibits higher absorption efficiency than chromium picolinate and chromium chloride in Caco-2 cell monolayersJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 2 2008L.-Y. Zha Summary This study was conducted to determine whether chromium nanoparticle (CrNano) exhibited higher absorption efficiency and possessed unique absorption mechanism in comparison to chromium picolinate (CrPic) and chromium chloride (CrCl3), as was postulated by previous reports. Twenty-one-day-old Caco-2 cell monolayers grown on semipermeable membranes in Snapwell tissue culture bichambers were incubated with CrNano, CrPic or CrCl3 to examine their transport and uptake respectively. In the concentration range of 0.2,20 ,mol/l, transport of CrNano, CrPic and CrCl3 across Caco-2 monolayers both in apical-to-basolateral and basolateral-to-apical direction was concentration-, and time-dependent, and temperature independent. The apparent permeability coefficient (Papp) of CrNano was between 5.89 and 7.92 × 10,6 cm/s and that of CrPic and CrCl3 was between 3.52 and 5.31 × 10,6 cm/s and between 0.97 and 1.37 × 10,6 cm/s respectively. Uptake of CrNano, CrPic and CrCl3 by both apical and basolateral membranes was concentration- and time-dependent. Uptake of CrNano by apical membrane was significantly (p < 0.05) decreased when the incubation temperature was reduced from 37 °C to 4 °C. The transport efficiency of CrNano, CrPic and CrCl3 after incubation for 120 min at 37 °C was 15.83% ± 0.76%, 9.08% ± 0.25% and 2.11% ± 0.53% respectively. The uptake efficiency of CrNano, CrPic and CrCl3 was 10.08% ± 0.76%, 4.73% ± 0.60% and 0.88% ± 0.08% respectively. It was concluded that the epithelial transport of CrNano, CrPic and CrCl3 across the Caco-2 cell monolayers was mainly via passive transport pathways. In addition, CrNano exhibited considerably higher absorption efficiency than both CrPic and CrCl3 in Caco-2 cell monolayers. [source] Renal glutathione transport: Identification of carriers, physiological functions, and controversiesBIOFACTORS, Issue 6 2009Lawrence H. Lash Abstract Glutathione (GSH) is an endogenous tripeptide composed of the amino acids L -glutamate, L -cysteine, and glycine. It is found in virtually all aerobic cells and plays critical roles in maintenance of cellular redox homeostasis and drug metabolism. An important component of its regulation is transport across biological membranes. Because GSH is a charged, hydrophilic molecule, transport occurs via catalysis by specific carrier proteins rather than by simple diffusion. Although it has been clearly understood that efflux of GSH across membranes such as the canalicular and sinusoidal plasma membranes in hepatocytes and the brush-border plasma membrane in renal proximal tubules is a key step in GSH turnover and interorgan metabolism, the existence and physiological functions of uptake of GSH across various epithelial plasma membranes has been subject to some debate. Besides transport across plasma membranes, GSH transport across intracellular membranes, most notably the mitochondrial inner membrane, has received some attention in recent years because of the importance of mitochondrial redox status and the mitochondrial GSH pool in cellular physiology and pathology. This commentary will focus on renal transport processes for GSH and will discuss some of the controversies that have existed and still seem to exist in the literature, specifically regarding uptake of intact GSH by basolateral membranes of renal proximal tubular cells and uptake of intact GSH by the mitochondrial inner membrane. © 2009 International Union of Biochemistry and Molecular Biology, Inc. [source] | |||||||||||||