Artículos de revistas: "Epithelialer Transport"

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CRANDALL, EDWARD D y MICHAEL A MATTHAY. "Alveolar Epithelial Transport". American Journal of Respiratory and Critical Care Medicine 163, n.º 4 (15 de marzo de 2001): 1021–29. http://dx.doi.org/10.1164/ajrccm.163.4.2006116.

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Saumon, G. y G. Basset. "Electrolyte and fluid transport across the mature alveolar epithelium". Journal of Applied Physiology 74, n.º 1 (1 de enero de 1993): 1–15. http://dx.doi.org/10.1152/jappl.1993.74.1.1.

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The lungs must be kept "dry" for efficient gas exchange. The mechanisms that contribute to clear alveoli from fetal lung fluid at birth are still present during adult life and allow recovery from alveolar flooding. It has recently been shown with the use of different approaches in vitro, as well as in vivo, that alveolar epithelium performs solute-coupled fluid transport. Fluid absorption from alveoli occurs chiefly as a result of active transepithelial Na+ transport. The mechanisms of Na+ transport have been partly elucidated; Na+ enters alveolar cells through apical Na+ channels and Na(+)-coupled solute transporters and is pumped out at the basolateral membrane by a Na(+)-K(+)-adenosinetriphosphatase (ATPase). Transepithelial Na+ transport and fluid absorption are stimulated by beta-adrenergic agonists, with adenosine 3',5'-cyclic monophosphate being the likely intracellular second messenger. K+ is probably secreted into alveoli because its concentration in the epithelial lining fluid is larger than expected for passive distribution. K+ channels have been described that, in conjunction with Na(+)-K(+)-ATP-ase, might provide pathways for active transport. Active proton secretion or bicarbonate absorption have been reported, which may explain the low pH of the alveolar epithelial lining fluid. It is probable that active solute transports are the main determinants of epithelial lining fluid depth and composition. A challenge for the future is to understand how this homeostasis is achieved.

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Sears, Patrick R., Wei-Ning Yin y Lawrence E. Ostrowski. "Continuous mucociliary transport by primary human airway epithelial cells in vitro". American Journal of Physiology-Lung Cellular and Molecular Physiology 309, n.º 2 (15 de julio de 2015): L99—L108. http://dx.doi.org/10.1152/ajplung.00024.2015.

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Mucociliary clearance (MCC) is an important innate defense mechanism that continuously removes inhaled pathogens and particulates from the airways. Normal MCC is essential for maintaining a healthy respiratory system, and impaired MCC is a feature of many airway diseases, including both genetic (cystic fibrosis, primary ciliary dyskinesia) and acquired (chronic obstructive pulmonary disease, bronchiectasis) disorders. Research into the fundamental processes controlling MCC, therefore, has direct clinical application, but has been limited in part due to the difficulty of studying this complex multicomponent system in vitro. In this study, we have characterized a novel method that allows human airway epithelial cells to differentiate into a mucociliary epithelium that transports mucus in a continuous circular track. The mucociliary transport device allows the measurement and manipulation of all features of mucociliary transport in a controlled in vitro system. In this initial study, the effect of ciliary beat frequency and mucus concentration on the speed of mucociliary transport was investigated.

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4

Cooper, Eugene R. y Gerald Kasting. "Transport across epithelial membranes". Journal of Controlled Release 6, n.º 1 (diciembre de 1987): 23–35. http://dx.doi.org/10.1016/0168-3659(87)90061-7.

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5

Larsen, Erik Hviid. "Hans Henriksen Ussing. 30 December 1911 — 22 December 2000". Biographical Memoirs of Fellows of the Royal Society 55 (enero de 2009): 305–35. http://dx.doi.org/10.1098/rsbm.2009.0002.

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Hans Ussing was born on 30 December 1911 at Sorø Academy in Denmark, where his father Dr Henrik Ussing was a lecturer and, as historian, a leading Danish folklorist. After his doctoral thesis in marine biology, Hans Ussing came to August Krogh's laboratory, where he studied protein turnover by using deuterium-labelled amino acids. After World War II, when radioactive isotopes of light elements became available for biological research, Ussing pioneered the development of epithelial physiology by introducing new concepts and theoretical tools, such as unidirectional fluxes, exchange diffusion, the flux-ratio equation, the shortcircuiting technique, solvent drag, anomalous solvent drag and the pre-steady-state flux ratio theorem. In studies on frog skin, combining electrophysiology and radioactive tracer technology, he provided the first unambiguous demonstration of active transport of sodium ions. His two-membrane hypothesis of active transport by frog skin initiated studies of epithelial transport at the cellular level in other organs and of the mechanisms of action of hormones and drugs. His discovery of paracellular ion transports bridged the physiology of high-resistance and low-resistance epithelia. With the Na + recirculation theory of isotonic transport he continued his studies of epithelial physiology until shortly before his death. Ussing's scientific research provided analytical methods and new insights of general applicability for the study of absorbing and secreting epithelia—of equal importance to biology and medicine. Hans Ussing died on 22 December 2000 after a short illness.

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McCarthy, K. M., M. Lam, L. Subramanian, R. Shakya, Z. Wu, E. E. Newton y N. E. Simister. "Effects of mutations in potential phosphorylation sites on transcytosis of FcRn". Journal of Cell Science 114, n.º 8 (15 de abril de 2001): 1591–98. http://dx.doi.org/10.1242/jcs.114.8.1591.

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The neonatal Fc receptor, FcRn, transports immunoglobulin G (IgG) across intestinal epithelial cells of suckling rats and mice from the lumenal surface to the serosal surface. In cell culture models FcRn transports IgG bidirectionally, but there are differences in the mechanisms of transport in the two directions. We investigated the effects of mutations in the cytoplasmic domain of FcRn on apical to basolateral and basolateral to apical transport of Fc across rat inner medullary collecting duct (IMCD) cells. Basolateral to apical transport did not depend upon determinants in the cytoplasmic domain. In contrast, an essentially tailless FcRn was markedly impaired in apical to basolateral transport. Using truncation and substitution mutants, we identified serine-313 and serine-319 as phosphorylation sites in the cytoplasmic domain of FcRn expressed in Rat1 fibroblasts. Mutations at Ser-319 did not affect transcytosis across IMCD cells. FcRn-S313A was impaired in apical to basolateral transcytosis to the same extent as tailless FcRn, whereas FcRn-S313D transported at wild-type levels. FcRn-S313A recycled more Fc to the apical medium than the wild-type receptor, suggesting that Ser-313 is required to allow FcRn to be diverted from an apical recycling pathway to a transcytotic pathway.

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Uchino, Hiroshi, Ikumi Tamai, Hikaru Yabuuchi, Kayoko China, Ken-ichi Miyamoto, Eiji Takeda y Akira Tsuji. "Faropenem Transport across the Renal Epithelial Luminal Membrane via Inorganic Phosphate Transporter Npt1". Antimicrobial Agents and Chemotherapy 44, n.º 3 (1 de marzo de 2000): 574–77. http://dx.doi.org/10.1128/aac.44.3.574-577.2000.

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ABSTRACT We previously showed that the mouse inorganic phosphate transporter Npt1 operates in the hepatic sinusoidal membrane transport of anionic drugs such as benzylpenicillin and mevalonic acid. In the present study, the mechanism of renal secretion of penem antibiotics was examined by using a Xenopus oocyte expression system. Faropenem (an oral penem antibiotic) was transported via Npt1 with a Michaelis-Menten constant of 0.77 ± 0.34 mM in a sodium-independent but chloride ion-sensitive manner. When the concentration of chloride ions was increased, the transport activity of faropenem by Npt1 was decreased. Since the concentration gradient of chloride ions is in the lumen-to-intracellular direction, faropenem is expected to be transported from inside proximal tubular cells to the lumen. So, we tested the release of faropenem from Xenopusoocytes. The rate of efflux of faropenem from Npt1-expressing oocytes was about 9.5 times faster than that from control water-injectedXenopus oocytes. Faropenem transport by Npt1 was significantly inhibited by β-lactam antibiotics such as benzylpenicillin, ampicillin, cephalexin, and cefazolin to 24.9, 40.5, 54.4, and 26.2% of that for the control, respectively. Zwitterionic β-lactam antibiotics showed lesser inhibitory effects on faropenem uptake than anionic derivatives, indicating that Npt1 preferentially transports anionic compounds. Other anionic compounds, such as indomethacin and furosemide, and the anion transport inhibitor 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid significantly inhibited faropenem uptake mediated by Npt1. In conclusion, our results suggest that Npt1 participates in the renal secretion of penem antibiotics.

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8

Van Itallie, Christina M. y James M. Anderson. "CLAUDINS AND EPITHELIAL PARACELLULAR TRANSPORT". Annual Review of Physiology 68, n.º 1 (enero de 2006): 403–29. http://dx.doi.org/10.1146/annurev.physiol.68.040104.131404.

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9

Harvey, Brian J. "Crosstalk and epithelial ion transport". Current Opinion in Nephrology and Hypertension 3, n.º 5 (septiembre de 1994): 523–28. http://dx.doi.org/10.1097/00041552-199409000-00008.

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10

Bucheimer, R. Elaine y Joel Linden. "Purinergic regulation of epithelial transport". Journal of Physiology 555, n.º 2 (23 de febrero de 2004): 311–21. http://dx.doi.org/10.1113/jphysiol.2003.056697.

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11

Warth, Richard. "Potassium channels in epithelial transport". Pflügers Archiv - European Journal of Physiology 446, n.º 5 (18 de abril de 2003): 505–13. http://dx.doi.org/10.1007/s00424-003-1075-2.

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12

Thomas, L. E., M. A. Rocafull y J. R. del Castillo. "Is the Second Sodium Pump Electrogenic?" BioMed Research International 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/698674.

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Transepithelial sodium transport is a process that involves active Na+transport at the basolateral membrane of the epithelial cell. This process is mediated by the Na+/K+pump, which exchanges 3 internal Na+by 2 external K+inducing a net charge movement and the second Na+pump, which transports Na+accompanied by Cl−and water. It has been suggested that this pump could also be electrogenic. Herein, we evaluated, in MDCK cells, the short-circuit current (Isc) generated by these Na+pumps at the basolateral membrane of the epithelial cells, using amphotericin B as an apical permeabilizing agent. In Cl−-containing media,Iscinduced by amphotericin B is totally inhibited by ouabain, indicating that only the electrogenic Na+/K+pump is detectable in the presence of Cl−. Electrogenicity of the second Na+pump can be demonstrated in Cl−-free media. The existence of a furosemide-sensitive component ofIsc, in addition to an ouabain-sensitive one, was identified in absence of chloride. Passive Cl−movement associated with the function of the second Na+pump seems to be regulated by the pump itself. These results demonstrate that the second Na+pump is an electroneutral mechanism result from the stoichiometric movement of Na+and Cl−across the basolateral plasma membrane of the epithelial cell.

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13

Marunaka, Yoshinori, Naomi Niisato, Akiyuki Taruno, Mariko Ohta, Hiroaki Miyazaki, Shigekuni Hosogi, Ken-ichi Nakajima et al. "Regulation of Epithelial Sodium Transport via Epithelial Na+Channel". Journal of Biomedicine and Biotechnology 2011 (2011): 1–8. http://dx.doi.org/10.1155/2011/978196.

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Renal epithelial Na+transport plays an important role in homeostasis of our body fluid content and blood pressure. Further, the Na+transport in alveolar epithelial cells essentially controls the amount of alveolar fluid that should be kept at an appropriate level for normal gas exchange. The epithelial Na+transport is generally mediated through two steps: (1) the entry step of Na+via epithelial Na+channel (ENaC) at the apical membrane and (2) the extrusion step of Na+via the Na+, K+-ATPase at the basolateral membrane. In general, the Na+entry via ENaC is the rate-limiting step. Therefore, the regulation of ENaC plays an essential role in control of blood pressure and normal gas exchange. In this paper, we discuss two major factors in ENaC regulation: (1) activity of individual ENaC and (2) number of ENaC located at the apical membrane.

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14

Suaud, Laurence, Wusheng Yan y Ronald C. Rubenstein. "Abnormal regulatory interactions of I148T-CFTR and the epithelial Na+channel inXenopusoocytes". American Journal of Physiology-Cell Physiology 292, n.º 1 (enero de 2007): C603—C611. http://dx.doi.org/10.1152/ajpcell.00088.2006.

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The mechanisms underlying regulatory interactions of the cystic fibrosis transmembrane conductance regulator (CFTR) and the epithelial Na+channel (ENaC) in Xenopus oocytes are controversial. CFTR's first nucleotide binding domain (NBD-1) may be important in these interactions, because mutations within NBD-1 impair these functional interactions. We hypothesized that an abnormal CFTR containing a non-NBD-1 mutation and able to transport chloride would retain regulatory interactions with murine ENaC (mENaC). We tested this hypothesis for I148T-CFTR, where the mutation is located in CFTR's first intracellular loop. I148T-CFTR has been associated with a severe CF phenotype, perhaps because of defects in its regulation of bicarbonate transport, but it transports chloride similarly to wild-type CFTR in model systems (Choi JY, Muallem D, Kiselyov K, Lee MG, Thomas PJ, Muallem S. Nature 410: 94–97, 2001). cRNAs encoding αβγ-mENaC and I148T-CFTR were injected separately or together into Xenopus oocytes. mENaC and CFTR functional expression were assessed by two-electrode voltage clamp. mENaC whole oocyte expression was determined by immunoblotting, and surface expression was quantitated by surface biotinylation. Injection of I148T-CFTR cRNA alone yielded high levels of CFTR functional expression. In coinjected oocytes, mENaC functional and surface expression was not altered by activation of I148T-CFTR with forskolin/ IBMX. Furthermore, the CFTR potentiator genistein both enhanced functional expression of I148T-CFTR and restored regulation of mENaC surface expression by activated I148T-CFTR. These data suggest that the ability to transport chloride is not a critical determinant of regulation of mENaC by activated CFTR in Xenopus oocytes and provide further evidence that I148T-CFTR is dysfunctional despite maintaining the ability to transport chloride.

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Li, Zhouhua, Liwei Wang, Thomas S. Hays y Yu Cai. "Dynein-mediated apical localization of crumbs transcripts is required for Crumbs activity in epithelial polarity". Journal of Cell Biology 180, n.º 1 (14 de enero de 2008): 31–38. http://dx.doi.org/10.1083/jcb.200707007.

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Asymmetrical localization of transcripts coupled with localized translation constitutes an important mechanism widely deployed to regulate gene activity in a spatial manner. The conserved transmembrane protein Crumbs (Crb) is an important regulator of epithelial polarity. However, it remains unclear how Crb is targeted to the apical domain. Here, we show that the cytoplasmic dynein complex transports both Crb protein and transcripts to the apical domain of Drosophila melanogaster follicular cells (FCs). The crb 3′ untranslated region (UTR) is necessary and sufficient for the apical localization of its transcript and this apical transcript localization is crucial for crb function. In crb mutant FCs, Crb protein derived from transgenes lacking the 3′ UTR does not effectively localize to the apical domain and does not effectively restore normal epithelial polarity. We propose that dynein-mediated messenger RNA transport coupled with a localized translation mechanism is involved in localizing Crb to the apical domain to mediate epithelial apicobasal polarity and that this mechanism might be widely used to regulate cellular polarity.

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HU, Huankai, Seiji MIYAUCHI, Christy C. BRIDGES, Sylvia B. SMITH y Vadivel GANAPATHY. "Identification of a novel Na+- and Cl−-coupled transport system for endogenous opioid peptides in retinal pigment epithelium and induction of the transport system by HIV-1 Tat". Biochemical Journal 375, n.º 1 (1 de octubre de 2003): 17–22. http://dx.doi.org/10.1042/bj20031059.

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The endogenous opioid peptides enkephalins, dynorphins and endorphins consist of five or more amino acids. These peptides participate in a multitude of biological functions in mammalian cells by interacting with different subtypes of opiate receptors located on the plasma membrane and in the nucleus. Here we report on the identification of a new peptide transport system in the human retinal pigment epithelial (RPE) cells that transports a variety of endogenous opioid peptides with high affinity. We identified this novel, hitherto unrecognized, transport system when we were analysing the differential effects of Tat, the transacting factor encoded by HIV-1, on various transport processes in RPE cells. This transport system is markedly induced by Tat. This opioid transport system is energized by transmembrane Na+ and Cl− gradients and is distinct from any of the previously identified transport systems for opioid peptides in mammalian cells. Free amino acids, dipeptides, tripeptides and non-peptide opiate receptor antagonists are excluded by this newly identified transport system. The affinities of endogenous opioid peptides for this system are in the range of 0.4–40 μM. The identification of the high-affinity Na+- and Cl−-coupled transport system in mammalian cells that is specific for endogenous opioid peptides and is induced by HIV-1 Tat is of significance not only to the biology of opioid peptides but also to the pathology of HIV-1 infection in humans.

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17

Goytain, Angela y Gary A. Quamme. "Functional characterization of human SLC41A1, a Mg2+transporter with similarity to prokaryotic MgtE Mg2+transporters". Physiological Genomics 21, n.º 3 (11 de mayo de 2005): 337–42. http://dx.doi.org/10.1152/physiolgenomics.00261.2004.

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We have begun to identify and characterize genes that are differentially expressed with low magnesium. One of these sequences conformed to the solute carrier SLC41A1. Real-time RT-PCR of RNA isolated from renal distal tubule epithelial [mouse distal convoluted tubule (MDCT)] cells cultured in low-magnesium media relative to normal media and in the kidney cortex of mice maintained on low-magnesium diets compared with those animals consuming normal diets confirmed that the SLC41A1 transcript is responsive to magnesium. Mouse SLC41A1 was cloned from MDCT cells, expressed in Xenopus laevis oocytes, and studied with two-electrode voltage-clamp studies. When expressed in oocytes, SLC41A1 mediates saturable Mg2+uptake with a Michaelis constant of 0.67 mM. Transport of Mg2+by SLC41A1 is rheogenic, voltage dependent, and not coupled to Na+or Cl−. Expressed SLC41A1 transports a range of other divalent cations: Mg2+, Sr2+, Zn2+, Cu2+, Fe2+, Co2+, Ba2+, and Cd2+. The divalent cations Ca2+, Mn2+, and Ni2+and the trivalent ion Gd3+did not induce currents nor did they inhibit Mg2+transport. The nonselective cation La3+abolished Mg2+uptake. The SLC41A1 transcript is present in many tissues, notably renal epithelial cells, and is upregulated in some tissues with magnesium deficiency. These studies suggest that SLC41A1 is a regulated Mg2+transporter that might be involved in magnesium homeostasis in epithelial cells.

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18

Hollenhorst, Monika I., Katrin Richter y Martin Fronius. "Ion Transport by Pulmonary Epithelia". Journal of Biomedicine and Biotechnology 2011 (2011): 1–16. http://dx.doi.org/10.1155/2011/174306.

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The lung surface of air-breathing vertebrates is formed by a continuous epithelium that is covered by a fluid layer. In the airways, this epithelium is largely pseudostratified consisting of diverse cell types such as ciliated cells, goblet cells, and undifferentiated basal cells, whereas the alveolar epithelium consists of alveolar type I and alveolar type II cells. Regulation and maintenance of the volume and viscosity of the fluid layer covering the epithelium is one of the most important functions of the epithelial barrier that forms the outer surface area of the lungs. Therefore, the epithelial cells are equipped with a wide variety of ion transport proteins, among which Na+, Cl−, and K+channels have been identified to play a role in the regulation of the fluid layer. Malfunctions of pulmonary epithelial ion transport processes and, thus, impairment of the liquid balance in our lungs is associated with severe diseases, such as cystic fibrosis and pulmonary oedema. Due to the important role of pulmonary epithelial ion transport processes for proper lung function, the present paper summarizes the recent findings about composition, function, and ion transport properties of the airway epithelium as well as of the alveolar epithelium.

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19

Stanke, Frauke. "The Contribution of the Airway Epithelial Cell to Host Defense". Mediators of Inflammation 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/463016.

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In the context of cystic fibrosis, the epithelial cell has been characterized in terms of its ion transport capabilities. The ability of an epithelial cell to initiate CFTR-mediated chloride and bicarbonate transport has been recognized early as a means to regulate the thickness of the epithelial lining fluid and recently as a means to regulate the pH, thereby determining critically whether or not host defense proteins such as mucins are able to fold appropriately. This review describes how the epithelial cell senses the presence of pathogens and inflammatory conditions, which, in turn, facilitates the activation of CFTR and thus directly promotes pathogens clearance and innate immune defense on the surface of the epithelial cell. This paper summarizes functional data that describes the effect of cytokines, chemokines, infectious agents, and inflammatory conditions on the ion transport properties of the epithelial cell and relates these key properties to the molecular pathology of cystic fibrosis. Recent findings on the role of cystic fibrosis modifier genes that underscore the role of the epithelial ion transport in host defense and inflammation are discussed.

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20

Islam, Rafiqul, Naohiko Anzai, Nesar Ahmed, Mohammad Ahtashamul Haque, Shamima Ferdous, Sagir Ahmed, MS Jahirul Haque Chowdhury et al. "Transport of Methylmercury through the Epithelial Type Amino Acid Transporter System B0". Journal of National Institute of Neurosciences Bangladesh 5, n.º 2 (7 de septiembre de 2019): 127–36. http://dx.doi.org/10.3329/jninb.v5i2.43017.

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Background: System B0 is a sodium dependent transporter that transports wide variety of neutral amino acids in the intestinal and renal proximal tubular epithelial cells. Methylmercury (MeHg) readily and non-enzymatically reacts with cysteine to form conjugate structurally similar to the amino acid methionine. Objective: In this study, we investigated the molecular mechanism of absorptive transport of MeHg in intestine using Xenopus oocytes expressing hB0AT1 and the uptake of metylmercry-Cys (MeHg-Cys) by heterodimeric amino acids transporter. Methodology: We confirmed the uptake of [14C] L-Leucine a potent substrate for the hB0AT1 amino acids transporter. The uptake of [14C] L-leucine by hB0AT1 was inhibited by MeHg-Cys conjugate, leucine, cysteine, methinine and phenylalanine in concentration–dependent manner. The IC50 of MeHg-Cys conjugate was significantly lower than that of leucine, cysteine, methinine and phenylalanine, indicating that hB0AT1 is a high affinity MeHg transporter. To assess MeHg-Cys conjugate transport, we measured [14C] MeHg uptake in Xenopus oocytes expressing hB0AT1 in presence or absence of sodium. The [14C] MeHg was transport only in the presence of cysteine and the transport was significantly sodium dependent and inhibited by a system B0 inhibitor 2-aminobicyclo-[2,21]- haptane-2-carboxylic acid (BCH). Result: The current findings indicate that hB0AT1 and heterodimeric amino acids absorb MeHg in the form of cysteine conjugate from the intestinal lumen across the brush-border membrane in to the cells and is supposed to be plays a critical role in the pathogenesis of Minamata disease and present results descried a major molecular mechanism by which MeHg is transported across cell membranes and indicate that metal complexes may form a novel class of substrates for amino acid carriers. Conclusion: In this experiment the results also suggest that uptake of Methionine and MeHg-Cys by heterodimeric amino acid transporter is significantly correlated where the uptake of Methionine and MeHg-Cys between heterodimeric amino acid transporter and hB0AT1 is not correlated. Journal of National Institute of Neurosciences Bangladesh, 2019;5(2): 127-136

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Han, Ki-Hwan, Kavya Mekala, Venetia Babida, Hye-Young Kim, Mary E. Handlogten, Jill W. Verlander y I. David Weiner. "Expression of the gas-transporting proteins, Rh B glycoprotein and Rh C glycoprotein, in the murine lung". American Journal of Physiology-Lung Cellular and Molecular Physiology 297, n.º 1 (julio de 2009): L153—L163. http://dx.doi.org/10.1152/ajplung.90524.2008.

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A family of gas-transporting proteins, the Mep/Amt/Rh glycoprotein family, has been identified recently. These are integral membrane proteins, are widely expressed in sites of gas transport, and are known to transport the gaseous molecule, NH3, and recent evidence indicates they can transport CO2. Because the mammalian lung is a critical site for gas transport, the current studies examine the expression of the nonerythroid members of this extended family, Rh B glycoprotein (Rhbg) and Rh C glycoprotein (Rhcg), in the normal mouse lung. Real-time RT-PCR and immunoblot analysis demonstrated both Rhbg and Rhcg mRNA and protein expression, respectively. Immunohistochemistry demonstrated both Rhbg and Rhcg were expressed in bronchial and bronchiolar epithelial cells. Rhbg was expressed by Clara cells, specifically, whereas all bronchial/bronchiolar epithelial cells, with the exception of goblet cells, expressed Rhcg. Rhbg expression was basolateral, whereas Rhcg exhibited apical and intracellular immunolabel, polarized expression similar to that observed in Rhbg- and Rhcg-expressing epithelial cells in other organs. There was no detectable expression of either Rhbg or Rhcg in alveolar endothelial or epithelial cells, in pneumocytes or in vascular tissue. In vitro studies using cultured bronchial epithelial cells confirm Rhbg and Rhcg expression, demonstrate that saturable, not diffusive, transport is the primary mechanism of ammonia/methylammonia transport, and show that the saturable transport mechanism has kinetics similar to those demonstrated previously for Rhbg and Rhcg. These findings suggest Rhbg and Rhcg may contribute to bronchial epithelial cell ammonia metabolism and suggest that they do not contribute to pulmonary CO2 transport.

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22

Imai, Yusuke. "Graphic Representation of Epithelial Transport System." membrane 27, n.º 1 (2002): 39–45. http://dx.doi.org/10.5360/membrane.27.39.

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23

de Sousa, R. C. "Effects of Vasopressin on Epithelial Transport". Journal of Cardiovascular Pharmacology 8 (1986): S23—S28. http://dx.doi.org/10.1097/00005344-198600087-00006.

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24

Quamme, Gary A. y R. Jean Shapiro. "Membrane controls of epithelial phosphate transport". Canadian Journal of Physiology and Pharmacology 65, n.º 3 (1 de marzo de 1987): 275–86. http://dx.doi.org/10.1139/y87-049.

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Phosphate homeostasis involves efficient intestinal absorption of dietary phosphate and sensitive renal conservation of filtered phosphate. Phosphate transport occurs by similar mechanisms across the intestinal and renal epithelium. This includes secondary active uptake across the brush-border membrane, movement of phosphate across the cytosol or into the metabolic phosphate pool, and finally the passive exit from the basolateral membrane. Active transport across the brush-border membrane involves cotransport of phosphate with sodium, which moves down its electrochemical gradient. As this process is the rate-limiting step, it is thought to be the controlling event in intestinal and renal absorption. The interaction of phosphate, sodium, and hydrogen ions with the recognition proteins involved with sodium-dependent phosphate transport is complex and not fully understood. Furthermore, the lipid bilayer structure may play a significant role in controlling the sequence of events in the movement across the brush-border membrane. Transfer of phosphate through the cytosol and exit across the basolateral membrane is less well understood, although the latter transmembrane flux is thought to be carrier mediated. Intestinal phosphate absorption is determined principally by plasma calcium and phosphate concentrations (1,25(OH)2 D3) and dietary availability of phosphate (intrinsic adaptation). On the other hand, renal conservation is determined by the available calcium (PTH), phosphate (intrinsic adaptation), and acid–base balance (hydrogen ions). These controls alter sodium-dependent phosphate cotransport across the brush-border membrane of the epithelial cell. The chemical alterations of the brush-border membrane and the metabolic events leading to changes in the brush-border membrane are not understood. The use of isolated, purified membranes and innovations of current techniques will enhance our understanding of these events and allow us to explain the mechanisms controlling epithelial phosphate absorption.

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25

Hernández, Julio A. "Reduced Dynamic Models in Epithelial Transport". Journal of Biophysics 2013 (28 de febrero de 2013): 1–9. http://dx.doi.org/10.1155/2013/654543.

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Most models developed to represent transport across epithelia assume that the cell interior constitutes a homogeneous compartment, characterized by a single concentration value of the transported species. This conception differs significantly from the current view, in which the cellular compartment is regarded as a highly crowded media of marked structural heterogeneity. Can the finding of relatively simple dynamic properties of transport processes in epithelia be compatible with this complex structural conception of the cell interior? The purpose of this work is to contribute with one simple theoretical approach to answer this question. For this, the techniques of model reduction are utilized to obtain a two-state reduced model from more complex linear models of transcellular transport with a larger number of intermediate states. In these complex models, each state corresponds to the solute concentration in an intermediate intracellular compartment. In addition, the numerical studies reveal that it is possible to approximate a general two-state model under conditions where strict reduction of the complex models cannot be performed. These results contribute with arguments to reconcile the current conception of the cell interior as a highly complex medium with the finding of relatively simple dynamic properties of transport across epithelial cells.

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Friedman, P. A. y F. A. Gesek. "Calcium transport in renal epithelial cells". American Journal of Physiology-Renal Physiology 264, n.º 2 (1 de febrero de 1993): F181—F198. http://dx.doi.org/10.1152/ajprenal.1993.264.2.f181.

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Extracellular calcium homeostasis involves coordinated calcium absorption by the intestine, calcium resorption from bone, and calcium reabsorption by the kidney. This review addresses the mechanism and regulation of renal calcium transport. Calcium reabsorption occurs throughout the nephron. However, distal tubules are the nephron site at which calcium reabsorption is regulated by parathyroid hormone, calcitonin, and 1 alpha,25-dihydroxyvitamin D3 and where the magnitude of net reabsorption is largely determined. These and related observations underscore the view that distal tubules are highly specialized to permit fine regulation of calcium excretion in response to alterations in extracellular calcium levels. Progress in understanding the mechanism and regulation of calcium transport has emerged from application of single cell fluorescence, patch clamp, and molecular biological approaches. These techniques permit the examination of ion transport at the cellular level and its regulation at subcellular and molecular levels. This editorial review focuses on recent and emerging observations and attempts to integrate them into models of cellular calcium transport.

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27

Layton, Anita T. "Recent advances in renal epithelial transport". American Journal of Physiology-Renal Physiology 316, n.º 2 (1 de febrero de 2019): F274—F276. http://dx.doi.org/10.1152/ajprenal.00510.2018.

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28

Santos, Javier y Mary H. Perdue. "Immunological Regulation of Intestinal Epithelial Transport". Digestion 59, n.º 4 (1998): 404–8. http://dx.doi.org/10.1159/000007498.

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29

Fritz, Jill M., Li Yang y Timothy E. Weaver. "Lipid transport and epithelial barrier integrity". Oncotarget 6, n.º 25 (22 de agosto de 2015): 20744–45. http://dx.doi.org/10.18632/oncotarget.5233.

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30

Bowman, B. B., D. B. McCormick y I. H. Rosenberg. "Epithelial Transport of Water-Soluble Vitamins". Annual Review of Nutrition 9, n.º 1 (julio de 1989): 187–99. http://dx.doi.org/10.1146/annurev.nu.09.070189.001155.

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31

Pearce, David. "SGK1 Regulation of Epithelial Sodium Transport". Cellular Physiology and Biochemistry 13, n.º 1 (2003): 13–20. http://dx.doi.org/10.1159/000070245.

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32

Szeberenyi, Jozsef. "Vectorial Transport in intestinal epithelial cells". Biochemistry and Molecular Biology Education 34, n.º 6 (noviembre de 2006): 449–51. http://dx.doi.org/10.1002/bmb.2006.494034062686.

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33

Gerencser, George A., Gregory A. Ahearn, Jianliang Zhang y Mark A. Cattey. "Sulfate transport mechanisms in epithelial systems". Journal of Experimental Zoology 289, n.º 4 (2001): 245–53. http://dx.doi.org/10.1002/1097-010x(20010401/30)289:4<245::aid-jez5>3.0.co;2-g.

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34

Shuttleworth, Trevor J. "Overview of epithelial ion-transport mechanisms". Canadian Journal of Zoology 67, n.º 12 (1 de diciembre de 1989): 3032–38. http://dx.doi.org/10.1139/z89-426.

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The basic cellular transport mechanisms for the transepithelial uptake and elimination of sodium and chloride ions are briefly reviewed. These frequently involve processes defined as secondary active mechanisms, and the problems that this creates for their identification in epithelial systems are emphasised. It is suggested that despite the wide range of epithelial tissues involved in body fluid ion regulation, current evidence indicates that a relatively limited group of these secondary active carriers is involved in the transport process, and the basis for this evolutionary conservatism is discussed, together with certain of its implications. Finally, the interactions of the transport mechanisms with metabolic and acid–base parameters are contrasted in ion-uptake and ion-excretion situations, and the possible roles of carbonic anhydrase compared.

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35

Folkesson, Hans G. y Michael A. Matthay. "Alveolar Epithelial Ion and Fluid Transport". American Journal of Respiratory Cell and Molecular Biology 35, n.º 1 (julio de 2006): 10–19. http://dx.doi.org/10.1165/rcmb.2006-0080sf.

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36

Yu, Alan S. L. "Evolving concepts in epithelial magnesium transport". Current Opinion in Nephrology and Hypertension 10, n.º 5 (septiembre de 2001): 649–53. http://dx.doi.org/10.1097/00041552-200109000-00016.

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37

Rojas, Raul y Gerard Apodaca. "Immunoglobulin transport across polarized epithelial cells". Nature Reviews Molecular Cell Biology 3, n.º 12 (diciembre de 2002): 944–56. http://dx.doi.org/10.1038/nrm972.

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38

SULLIVAN, LAWRENCE P., DARREN P. WALLACE y JARED J. GRANTHAM. "Epithelial Transport in Polycystic Kidney Disease". Physiological Reviews 78, n.º 4 (1 de octubre de 1998): 1165–91. http://dx.doi.org/10.1152/physrev.1998.78.4.1165.

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Sullivan, Lawrence P., Darren P. Wallace, and Jared J. Grantham. Epithelial Transport in Polycystic Kidney Disease. Physiol. Rev. 78: 1165–1191, 1998. — In autosomal dominant polycystic kidney disease (ADPKD), the genetic defect results in the slow growth of a multitude of epithelial cysts within the renal parenchyma. Cysts originate within the glomeruli and all tubular structures, and their growth is the result of proliferation of incompletely differentiated epithelial cells and the accumulation of fluid within the cysts. The majority of cysts disconnect from tubular structures as they grow but still accumulate fluid within the lumen. The fluid accumulation is the result of secretion of fluid driven by active transepithelial Cl− secretion. Proliferation of the cells and fluid secretion are activated by agonists of the cAMP signaling pathway. The transport mechanisms involved include the cystic fibrosis transmembrane conductance regulator (CFTR) present in the apical membrane of the cystic cells and a bumetanide-sensitive transporter located in the basolateral membrane. A lipid factor, called cyst activating factor, has been found in the cystic fluid. Cyst activating factor stimulates cAMP production, proliferation, and fluid secretion by cultured renal epithelial cells and also is a chemotactic agent. Cysts also appear in the intrahepatic biliary tree in ADPKD. Normal ductal cells secrete Cl− and HCO− 3. The cystic ductal cell also secretes Cl−, but HCO− 3 secretion is diminished, probably as the result of a lower population of Cl−/HCO− 3 exchangers in the apical membrane as compared with the normal cells. Some segments of the normal renal tubule are also capable of utilizing CFTR to secrete Cl−, particularly the inner medullary collecting duct. The ability of Madin-Darby canine kidney cells and normal human kidney cortex cells to form cysts in culture and to secrete fluid and the functional similarities between these incompletely differentiated, proliferative cells and developing cells in the intestinal crypt and in the fetal lung have led us to suggest that Cl− and fluid secretion may be a common property of at least some renal epithelial cells in an intermediate stage of development. The genetic defect in ADPKD may not directly affect membrane transport mechanisms but rather may arrest the development of certain renal epithelial cells in an incompletely differentiated, proliferative stage.

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39

Clauss, Wolfgang G. "Epithelial transport and osmoregulation in annelids". Canadian Journal of Zoology 79, n.º 2 (1 de febrero de 2001): 192–203. http://dx.doi.org/10.1139/z00-200.

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Epithelial transport related to osmoregulation has so far not been extensively investigated in annelids. Compared with the large body of information about ion transport across crustacean or insect epithelia, only a few studies have been done with isolated preparations of annelids, using the body wall of marine polychaetes or Hirudinea. Nephridial function and general body homeostasis have received more attention, and have probably been best investigated in Hirudinea. With recent advances in the molecular physiology of epithelial transport systems in vertebrates, the cloning of various transporters and ion channels, and the considerable number of osmoregulatory peptides that have now been found and analyzed from annelids, it should now be possible, and is timely, to conduct functional studies on individual selected epithelial preparations or isolated cells from annelids. Such studies may be important for establishing useful models with somewhat less complexity than mammalian systems. For example, annelids lack aldosterone, an important osmoregulatory hormone, which is a key factor in the regulation of sodium reabsorption in vertebrates. Therefore, not only would such studies contribute to annelid physiology, but they would be important in a broader sense for understanding osmoregulation and its evolution. They should also facilitate the discovery and investigation of new specific regulatory pathways.

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40

Welsh, Michael J. "Mechanisms of Airway Epithelial Ion Transport". Clinics in Chest Medicine 7, n.º 2 (junio de 1986): 273–83. http://dx.doi.org/10.1016/s0272-5231(21)00423-8.

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41

Bastian, SE, PE Walton, FJ Ballard y DA Belford. "Transport of IGF-I across epithelial cell monolayers". Journal of Endocrinology 162, n.º 3 (1 de septiembre de 1999): 361–69. http://dx.doi.org/10.1677/joe.0.1620361.

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Epithelial cells line the lumens of organs including the gastrointestinal tract, kidney tubules and respiratory airways, where they regulate the transport of electrolytes and the movement of macromolecules. The current study aimed to investigate the transport of IGF-I across epithelial cell barriers. Epithelial cell lines derived from gut (IEC-6), kidney (MDBK) and lung (Mv1Lu) were shown to possess high-affinity, functional receptors for IGF-I and formed tight junctions in monolayer culture. To investigate the transport of IGF-I, the three cell lines were grown on microporous filters in a bi-chamber system. In comparison with filters without cells, IEC-6 and Mv1Lu epithelial cell monolayers restricted the passage of (125)I-IGF-I and [(3)H]inulin, whereas the MDBK cells virtually occluded any passage of these molecules. Transport of (125)I-IGF-I across the epithelial cell monolayers was significantly less than that of [(3)H]inulin, suggesting that the binding of (125)I-IGF-I to high-affinity IGF receptors or IGF-binding proteins retarded its transport. Moreover, (125)I-IGF-I transport was not inhibited by the presence of excess unlabelled IGF-I. Our findings provide evidence for the restricted diffusion of intact, free IGF-I across gut, kidney and lung epithelial cell monolayers via a paracellular or low-affinity transcellular pathway.

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42

Caldwell, Ray A., Richard C. Boucher y M. Jackson Stutts. "Neutrophil elastase activates near-silent epithelial Na+channels and increases airway epithelial Na+transport". American Journal of Physiology-Lung Cellular and Molecular Physiology 288, n.º 5 (mayo de 2005): L813—L819. http://dx.doi.org/10.1152/ajplung.00435.2004.

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Neutrophil elastase is a serine protease that is abundant in the airways of individuals with cystic fibrosis (CF), a genetic disease manifested by excessive airway Na+absorption and consequent depletion of the airway surface liquid layer. Although endogenous epithelium-derived serine proteases regulate epithelial Na+transport, the effects of neutrophil elastase on epithelial Na+transport and epithelial Na+channel (ENaC) activity are unknown. Low micromolar concentrations of human neutrophil elastase (hNE) applied to the apical surface of a human bronchial cell line (16HBE14o-/βγ) increased Na+transport about twofold. Similar effects were observed with trypsin, also a serine protease. Proteolytic inhibitors of hNE or trypsin selectively abolished the enzyme-induced increase of epithelial Na+transport. At the level of the single channel, submicromolar concentrations of hNE increased activity of near-silent ENaC ∼108-fold in patches from NIH-3T3 cells expressing rat α-, β-, and γ-ENaC subunits. However, no enzyme effects were observed on basally active ENaCs. Trypsin exposure following hNE revealed no additional increase in amiloride-sensitive short-circuit current or in ENaC activity, suggesting these enzymes share a common mode of action for increasing Na+transport, likely through proteolytic activation of ENaC. The hNE-induced increase of near-silent ENaC activity in CF airways could contribute to Na+hyperabsorption, reduced airway surface liquid height, and dehydrated mucus culminating in inefficient mucociliary clearance.

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43

Haase, Melanie, Mandy Laube y Ulrich H. Thome. "Sex-specific effects of sex steroids on alveolar epithelial Na+ transport". American Journal of Physiology-Lung Cellular and Molecular Physiology 312, n.º 3 (1 de marzo de 2017): L405—L414. http://dx.doi.org/10.1152/ajplung.00275.2016.

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Alveolar fluid clearance mediates perinatal lung transition to air breathing in newborn infants, which is accomplished by epithelial Na+ channels (ENaC) and Na-K-ATPase. Male sex represents a major risk factor for developing respiratory distress, especially in preterm infants. We previously showed that male sex is associated with reduced epithelial Na+ transport, possibly contributing to the sexual dimorphism in newborn respiratory distress. This study aimed to determine sex-specific effects of sex steroids on epithelial Na+ transport. The effects of testosterone, 5α-dihydrotestosterone (DHT), estradiol, and progesterone on Na+ transport and Na+ channel expression were determined in fetal distal lung epithelial (FDLE) cells of male and female rat fetuses by Ussing chamber and mRNA expression analyses. DHT showed a minor effect only in male FDLE cells by decreasing epithelial Na+ transport. However, flutamide, an androgen receptor antagonist, did not abolish the gender imbalance, and testosterone lacked any effect on Na+ transport in male and female FDLE cells. In contrast, estradiol and progesterone increased Na+ transport and Na+ channel expression especially in females, and prevented the inhibiting effect of DHT in males. Estrogen receptor inhibition decreased Na+ channel expression and eliminated the sex differences. In conclusion, female sex steroids stimulate Na+ transport especially in females and prevent the inhibitory effect of DHT in males. The ineffectiveness of testosterone suggests that Na+ transport is largely unaffected by androgens. Thus, the higher responsiveness of female cells to female sex steroids explains the higher Na+ transport activity, possibly leading to a functional advantage in females.

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44

Schnúr, Andrea, Péter Hegyi, Simon Rousseau, Gergely L. Lukacs y Guido Veit. "Epithelial Anion Transport as Modulator of Chemokine Signaling". Mediators of Inflammation 2016 (2016): 1–20. http://dx.doi.org/10.1155/2016/7596531.

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The pivotal role of epithelial cells is to secrete and absorb ions and water in order to allow the formation of a luminal fluid compartment that is fundamental for the epithelial function as a barrier against environmental factors. Importantly, epithelial cells also take part in the innate immune system. As a first line of defense they detect pathogens and react by secreting and responding to chemokines and cytokines, thus aggravating immune responses or resolving inflammatory states. Loss of epithelial anion transport is well documented in a variety of diseases including cystic fibrosis, chronic obstructive pulmonary disease, asthma, pancreatitis, and cholestatic liver disease. Here we review the effect of aberrant anion secretion with focus on the release of inflammatory mediators by epithelial cells and discuss putative mechanisms linking these transport defects to the augmented epithelial release of chemokines and cytokines. These mechanisms may contribute to the excessive and persistent inflammation in many respiratory and gastrointestinal diseases.

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45

Bröer, S., J. A. Cavanaugh y J. E. J. Rasko. "Neutral amino acid transport in epithelial cells and its malfunction in Hartnup disorder". Biochemical Society Transactions 33, n.º 1 (1 de febrero de 2005): 233–36. http://dx.doi.org/10.1042/bst0330233.

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Hartnup disorder is an autosomal recessive abnormality of renal and gastrointestinal neutral amino acid transport. A corresponding transport activity has been characterized in kidney and intestinal cells and named system B0. The failure to resorb amino acids in this disorder is thought to be compensated by a protein-rich diet. However, in combination with a poor diet and other factors, more severe symptoms can develop in Hartnup patients, including a photosensitive pellagra-like skin rash, cerebellar ataxia and other neurological symptoms. Homozygosity mapping in a Japanese family and linkage analysis on six Australian pedigrees placed the Hartnup disorder gene at a locus on chromosome 5p15. This fine mapping facilitated a candidate gene approach within the interval, which resulted in the cloning and characterization of a novel member of the sodium-dependent neurotransmitter transporter family (B0AT1, SLC6A19) from mouse and human kidney, which shows all properties of system B0. Flux experiments and electrophysiological recording showed that the transporter is Na+ dependent and Cl− independent, electrogenic and actively transports most neutral amino acids. In situ hybridization showed strong expression in intestinal villi and in the proximal tubule of the kidney. Expression of B0AT1 was restricted to kidney, intestine and skin. A total of ten mutations have been identified in SLC6A19 that co-segregate with disease in the predicted recessive manner, with the majority of affected individuals being compound heterozygotes. These mutations lead to altered neutral amino acid transport function compared to the wild-type allele in vitro. One of the mutations occurs in members of the original Hartnup family described in 1956, thereby defining SLC6A19 as the ‘Hartnup’-gene.

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46

Compeau, C. G., O. D. Rotstein, H. Tohda, Y. Marunaka, B. Rafii, A. S. Slutsky y H. O'Brodovich. "Endotoxin-stimulated alveolar macrophages impair lung epithelial Na+ transport by an L-Arg-dependent mechanism". American Journal of Physiology-Cell Physiology 266, n.º 5 (1 de mayo de 1994): C1330—C1341. http://dx.doi.org/10.1152/ajpcell.1994.266.5.c1330.

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The Na+ transport function of alveolar epithelium represents an important mechanism for air space fluid clearance after acute lung injury. We studied the effect of endotoxin-stimulated rat alveolar macrophages on lung epithelial ion transport and permeability in vitro. Cultured rat distal lung (alveolar) epithelial monolayers incubated with both endotoxin and macrophages demonstrated a 75% decline in transepithelial resistance and a selective 60% reduction in amiloride-sensitive short-circuit current (Isc). Single-channel patch-clamp analysis demonstrated a 60% decrease in the density of 25-pS nonselective cation (NSC) channels on the apical membrane of epithelium exposed to both endotoxin and macrophages. A concurrent reduction in epithelial F-actin content suggested a role for actin depolymerization in mediating this effect. Incubation of cocultures with the methylated L-arginine (Arg) derivative NG-monomethyl-L-arginine prevented the reduction in epithelial Isc, as did substitution of L-Arg with D-Arg or incubation in L-Arg-free medium. Furthermore, the stable and products of Arg metabolism were found to have no effect on epithelial ion transport. These studies show that endotoxin-stimulated alveolar macrophages impair distal lung epithelial ion transport by an L-Arg-dependent mechanism by inactivating amiloride-sensitive 25-pS NSC channels. This may represent a novel mechanism whereby local inflammatory cells regulate lung epithelial ion transport. This could affect the ability of the lung to clear fluid from the air space.

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47

Bridges, Michael A., David C. Walker, Robert A. Harris, Bruce R. Wilson y A. George F. Davidson. "Cultured human nasal epithelial multicellular spheroids: polar cyst-like model tissues". Biochemistry and Cell Biology 69, n.º 2-3 (1 de febrero de 1991): 102–8. http://dx.doi.org/10.1139/o91-016.

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We report here a new readily cultured nonadherent hollow spheroidal epithelial tissue model: human nasal epithelial multicellular spheroids, prepared from brushings of human nasal epithelium in vivo. Although cultured cyst-like epithelial models developed from embryonic, transformed, or polypoid tissues have been reported previously, human nasal epithelial multicellular spheroids are derived from normal mature nontransformed human airway epithelial cells. In our studies, spheroids ranged in size from 50 to 700 μm diameter (averaging approximately 250 μm). Cells of the spheroid displayed morphological polarity and formed junctional complexes. Transcellular electrolyte transport may underlie the increase in spheroid size which occurred in culture. The ease and simplicity of the brushing and culture procedures reported here render normal and diseased human cell populations more readily accessible to investigation. We believe human nasal epithelial multicellular spheroids may have important applications in the study of electrolyte and fluid transport processes, ciliary motility, epithelial polarity, cellular metabolism, and drug cytotoxicity in normal and pathophysiological states of the human respiratory tract (e.g., cystic fibrosis).Key words: cultured airway epithelial cells, electrolyte and fluid transport, spheroid, cyst, cystic fibrosis.

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48

Weinstein, A. M. "Modeling the proximal tubule: complications of the paracellular pathway". American Journal of Physiology-Renal Physiology 254, n.º 3 (1 de marzo de 1988): F297—F305. http://dx.doi.org/10.1152/ajprenal.1988.254.3.f297.

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When the proximal tubule epithelium is represented as cellular and lateral intercellular (LIS) compartments, the presence of a paracellular pathway can render the overall phenomenologic equations quite an indirect representation of intraepithelial transport processes. 1) Active sodium transport into the LIS may create a hypertonic region that drives water movement from lumen to peritubular blood, i.e., a term for active water transport may appear in the overall transport equations. The correlate of this uphill water flux is a solute polarization effect, such that the measured epithelial water permeability is less than that of the cell membranes. 2) Basolateral uptake of potassium by the cell may lower the LIS concentration and promote diffusive entry of K across the tight junction. Even without cellular uptake of K from the lumen, the epithelial transport equations may contain a term for active K reabsorption. The solute polarization correlate is a low epithelial reflection coefficient that does not represent a convective flux of K through a specific channel. 3) When there is convective flux of Na and Cl through the tight junction but none through the cell, then a fluid circuit around junction and cell may be present, even when net epithelial volume flux is absent. In this case, part of the net epithelial Cl flux must be represented in the overall transport equations as electroneutral Na-Cl cotransport.

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49

Carpenter, Todd C., Stacey Schomberg, Christopher Nichols, Kurt R. Stenmark y John V. Weil. "Hypoxia reversibly inhibits epithelial sodium transport but does not inhibit lung ENaC or Na-K-ATPase expression". American Journal of Physiology-Lung Cellular and Molecular Physiology 284, n.º 1 (1 de enero de 2003): L77—L83. http://dx.doi.org/10.1152/ajplung.00181.2002.

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Hypoxia reduces alveolar liquid clearance and the nasal potential difference, a marker of airway epithelial sodium transport. The mechanisms underlying this impaired epithelial sodium transport in vivo remain uncertain. We hypothesized that epithelial sodium transport impaired by hypoxia would recover quickly with reoxygenation and that hypoxia decreases the expression of lung epithelial sodium channels and Na,K-ATPases. We studied adult rats exposed to normoxia, hypoxia (Fi O2 = 0.1) for 24 h, or hypoxia followed by recovery in normoxia. Nasal potential differences decreased by 40% with hypoxia ( P < 0.001), returning to baseline levels with reoxygenation. Lung Na,K-ATPase activity decreased by 40% with hypoxia ( P = 0.003), recovering to baseline levels with reoxygenation. Lung expression of mRNA encoding for epithelial sodium channel (ENaC)-α, -β, and -γ or for Na,K-ATPase-α1 did not change significantly with hypoxia or recovery nor did lung expression of ENaC-α, ENaC-β, Na,K-ATPase-α1, or Na,K-ATPase-β1 protein. We conclude that subacute exposure to moderate hypoxia reversibly impairs airway epithelial sodium transport and lung Na,K-ATPase activity but that those changes are not due to changes in the lung expression of sodium-transporting proteins.

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50

Beyenbach, Klaus W. "Energizing Epithelial Transport with the Vacuolar H+-ATPase". Physiology 16, n.º 4 (agosto de 2001): 145–51. http://dx.doi.org/10.1152/physiologyonline.2001.16.4.145.

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The Ussing model has long provided the conceptual foundation for understanding epithelial transport mechanisms energized by the Na+-K+-ATPase. Plasma membranes may also use the vacuolar (V-type) H+-ATPase as the primary energy source of membrane and epithelial transport. A pure electrogenic pump, the V-type H+-ATPase energizes not only membranes it inhabits but also other transport pathways via electrical coupling.

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