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Fournier E, Roussel C, Dominicis A, Ley D, Peyron MA, Collado V, Mercier-Bonin M, Lacroix C, Alric M, Van de Wiele T, Chassard C, Etienne-Mesmin L, Blanquet-Diot S. In vitro models of gut digestion across childhood: current developments, challenges and future trends. Biotechnol Adv 2021; 54:107796. [PMID: 34252564 DOI: 10.1016/j.biotechadv.2021.107796] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 07/05/2021] [Accepted: 07/06/2021] [Indexed: 02/08/2023]
Abstract
The human digestion is a multi-step and multi-compartment process essential for human health, at the heart of many issues raised by academics, the medical world and industrials from the food, nutrition and pharma fields. In the first years of life, major dietary changes occur and are concomitant with an evolution of the whole child digestive tract anatomy and physiology, including colonization of gut microbiota. All these phenomena are influenced by child exposure to environmental compounds, such as drugs (especially antibiotics) and food pollutants, but also childhood infections. Due to obvious ethical, regulatory and technical limitations, in vivo approaches in animal and human are more and more restricted to favor complementary in vitro approaches. This review summarizes current knowledge on the evolution of child gut physiology from birth to 3 years old regarding physicochemical, mechanical and microbial parameters. Then, all the available in vitro models of the child digestive tract are described, ranging from the simplest static mono-compartmental systems to the most sophisticated dynamic and multi-compartmental models, and mimicking from the oral phase to the colon compartment. Lastly, we detail the main applications of child gut models in nutritional, pharmaceutical and microbiological studies and discuss the limitations and challenges facing this field of research.
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Affiliation(s)
- Elora Fournier
- Université Clermont Auvergne, INRAE, UMR 454 MEDIS, Microbiologie Environnement Digestif et Santé, CRNH Auvergne, 63000 Clermont-Ferrand, France; Toxalim, Research Centre in Food Toxicology, INRAE, ENVT, INP-Purpan, UPS, Université de Toulouse, 31000 Toulouse, France
| | - Charlène Roussel
- Laval University, INAF Institute of Nutrition and Functional Foods, G1V 0A6 Quebec, Canada
| | - Alessandra Dominicis
- European Reference Laboratory for E. coli, Istituto Superiore di Sanità, Rome, Italy
| | - Delphine Ley
- Université Lille 2, Faculté de Médecine, Inserm U995 Nutritional Modulation of Infection and Inflammation, 59045 Lille, France
| | - Marie-Agnès Peyron
- Université Clermont Auvergne, INRAE, UNH, Unité de Nutrition Humaine, CRNH Auvergne, 63000 Clermont-Ferrand, France
| | - Valérie Collado
- Université Clermont Auvergne, EA 4847, CROC, Centre de Recherche en Odontologie Clinique, 63000 Clermont-Ferrand, France
| | - Muriel Mercier-Bonin
- Toxalim, Research Centre in Food Toxicology, INRAE, ENVT, INP-Purpan, UPS, Université de Toulouse, 31000 Toulouse, France
| | - Christophe Lacroix
- Laboratory of Food Biotechnology, Institute of Food, Nutrition and Health, ETH Zurich, 8092 Zürich, Switzerland
| | - Monique Alric
- Université Clermont Auvergne, INRAE, UMR 454 MEDIS, Microbiologie Environnement Digestif et Santé, CRNH Auvergne, 63000 Clermont-Ferrand, France
| | - Tom Van de Wiele
- Ghent University, Center for Microbial Ecology and Technology (CMET), Coupure Links 653, 9000 Ghent, Belgium
| | - Christophe Chassard
- Université Clermont Auvergne, INRAE, VetAgro Sup, UMRF, 15000 Aurillac, France
| | - Lucie Etienne-Mesmin
- Université Clermont Auvergne, INRAE, UMR 454 MEDIS, Microbiologie Environnement Digestif et Santé, CRNH Auvergne, 63000 Clermont-Ferrand, France
| | - Stéphanie Blanquet-Diot
- Université Clermont Auvergne, INRAE, UMR 454 MEDIS, Microbiologie Environnement Digestif et Santé, CRNH Auvergne, 63000 Clermont-Ferrand, France.
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Fetal Physiologically Based Pharmacokinetic Models: Systems Information on the Growth and Composition of Fetal Organs. Clin Pharmacokinet 2020; 58:235-262. [PMID: 29987449 DOI: 10.1007/s40262-018-0685-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
BACKGROUND The growth of fetal organs is a dynamic process involving considerable changes in the anatomical and physiological parameters that can alter fetal exposure to xenobiotics in utero. Physiologically based pharmacokinetic models can be used to predict the fetal exposure as time-varying parameters can easily be incorporated. OBJECTIVE The objective of this study was to collate, analyse and integrate the available time-varying parameters needed for the physiologically based pharmacokinetic modelling of xenobiotic kinetics in a fetal population. METHODS We performed a comprehensive literature search on the physiological development of fetal organs. Data were carefully assessed, integrated and a meta-analysis was performed to establish growth trends with fetal age and weight. Algorithms and models were generated to describe the growth of these parameter values as functions of age and/or weight. RESULTS Fetal physiologically based pharmacokinetic parameters, including the size of the heart, liver, brain, kidneys, lungs, spleen, muscles, pancreas, skin, bones, adrenal and thyroid glands, thymus, gut and gonads were quantified as a function of fetal age and weight. Variability around the means of these parameters at different fetal ages was also reported. The growth of the investigated parameters was not consistent (with respect to direction and monotonicity). CONCLUSION Despite the limitations identified in the availability of some values, the data presented in this article provide a unique resource for age-dependent organ size and composition parameters needed for fetal physiologically based pharmacokinetic modelling. This will facilitate the application of physiologically based pharmacokinetic models during drug development and in the risk assessment of environmental chemicals and following maternally administered drugs or unintended exposure to environmental toxicants in this population.
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To VPTH, Masagounder K, Loewen ME. SLC transporters ASCT2, B 0 AT1-like, y + LAT1, and LAT4-like associate with methionine electrogenic and radio-isotope flux kinetics in rainbow trout intestine. Physiol Rep 2019; 7:e14274. [PMID: 31705630 PMCID: PMC6841986 DOI: 10.14814/phy2.14274] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Accepted: 09/21/2019] [Indexed: 01/08/2023] Open
Abstract
Methionine (Met) is an important building block and metabolite for protein biosynthesis. However, the mechanism behind its absorption in the fish gut has not been elucidated. Here, we describe the fundamental properties of Met transport along trout gut at µmol/L and mmol/L concentration. Both electrogenic and unidirectional DL-[14 C]Met flux were employed to characterize Met transporters in Ussing chambers. Exploiting the differences in gene expression between diploid (2N) and triploid (3N) and intestinal segment as tools, allowed the association between gene and methionine transport. Specifically, three intestinal segments including pyloric caeca (PC), midgut (MG), and hindgut (HG) were assessed. Results at 0-150 µmol/L concentration demonstrated that the DL-Met was most likely transported by apical transporter ASCT2 (SLC1A5) and recycled by basolateral transporter y+ LAT1 (SLC7A7) due to five lines of observation: (1) lack of Na+ -independent kinetics, (2) low expression of B0 AT2-like gene, (3) Na+ -dependent, high-affinity (Km , µmol/L ranges) kinetics in DL-[14 C]Met flux, (4) association mRNA expression with the high-affinity kinetics and (5) electrogenic currents induced by Met. Results at 0.2-20 mmol/L concentration suggested that the DL-Met transport is likely transported by B0 AT1-like (SLC6A19-like) based on gene expression, Na+ -dependence and low-affinity kinetics (Km , mmol/L ranges). Similarly, genomic and gene expression analysis suggest that the basolateral exit of methionine was primarily through LAT4-like transporter (SLC43A2-like). Conclusively, DL-Met uptake in trout gut was most likely governed by Na+ -dependent apical transporters ASCT2 and B0 AT1-like and released through basolateral LAT4-like, with some recycling through y+ LAT1. A comparatively simpler model than that previously described in mammals.
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Affiliation(s)
- Van P. T. H. To
- Veterinary Biomedical SciencesUniversity of SaskatchewanSaskatoonSaskatchewanCanada
| | | | - Matthew E. Loewen
- Veterinary Biomedical SciencesUniversity of SaskatchewanSaskatoonSaskatchewanCanada
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Boudry G, David ES, Douard V, Monteiro IM, Le Huërou-Luron I, Ferraris RP. Role of intestinal transporters in neonatal nutrition: carbohydrates, proteins, lipids, minerals, and vitamins. J Pediatr Gastroenterol Nutr 2010; 51:380-401. [PMID: 20808244 DOI: 10.1097/mpg.0b013e3181eb5ad6] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
To support rapid growth and a high metabolic rate, infants require enormous amounts of nutrients. The small intestine must have the complete array of transporters that absorb the nutrients released from digested food. Failure of intestinal transporters to function properly often presents symptoms as "failure to thrive" because nutrients are not absorbed and as diarrhea because unabsorbed nutrients upset luminal osmolality or become substrates of intestinal bacteria. We enumerate the nutrients that constitute human milk and various infant milk formulas, explain their importance in neonatal nutrition, then describe for each nutrient the transporter(s) that absorbs it from the intestinal lumen into the enterocyte cytosol and from the cytosol to the portal blood. More than 100 membrane and cytosolic transporters are now thought to facilitate absorption of minerals and vitamins as well as products of digestion of the macronutrients carbohydrates, proteins, and lipids. We highlight research areas that should yield information needed to better understand the important role of these transporters during normal development.
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Affiliation(s)
- Gaëlle Boudry
- Institut National de Recherche Agronomique, UMR1079 Système d'Elevage, Nutrition, Animale et Humaine, St-Gilles, France
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Drozdowski LA, Clandinin T, Thomson ABR. Ontogeny, growth and development of the small intestine: Understanding pediatric gastroenterology. World J Gastroenterol 2010; 16:787-99. [PMID: 20143457 PMCID: PMC2825325 DOI: 10.3748/wjg.v16.i7.787] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Throughout our lifetime, the intestine changes. Some alterations in its form and function may be genetically determined, and some are the result of adaptation to diet, temperature, or stress. The critical period programming of the intestine can be modified, such as from subtle differences in the types and ratios of n3:m6 fatty acids in the diet of the pregnant mother, or in the diet of the weanlings. This early forced adaptation may persist in later life, such as the unwanted increased intestinal absorption of sugars, fatty acids and cholesterol. Thus, the ontogeny, early growth and development of the intestine is important for the adult gastroenterologist to appreciate, because of the potential for these early life events to affect the responsiveness of the intestine to physiological or pathological challenges in later life.
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Martín-Venegas R, Rodríguez-Lagunas MJ, Mercier Y, Geraert PA, Ferrer R. Effect of pH onl- andd-methionine uptake across the apical membrane of Caco-2 cells. Am J Physiol Cell Physiol 2009; 296:C632-8. [DOI: 10.1152/ajpcell.00478.2008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The transport systems involved in intestinal methionine (Met) absorption are described as Na+-dependent and Na+-independent mechanisms. However, since recent studies have suggested the importance of the H+gradient as a driving force for intestinal nutrient absorption, the aim of the present work was to test whether Met transport across the apical membrane of Caco-2 cells is affected by extracellular pH. The results show that l- and d-Met uptake was increased by lowering extracellular pH from 7.4 to 5.5, in both the presence and absence of Na+. Cis-inhibition experiments revealed that inhibition of l-Met transport by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) or l-lysine (l-Lys) was higher at a pH of 5.5. Moreover, the BCH-insensitive component was not affected by pH, whereas the l-Lys-insensitive component was increased by lowering extracellular pH, thus suggesting the participation of system L. The contribution of another mechanism, sensitive to both BCH and l-Lys, was also considered. The inhibition obtained with taurine (Tau) was also higher at a pH of 5.5, thus suggesting the involvement of system B0,+on pH-stimulated component. As for d-Met uptake, the results showed higher inhibition with l-Lys and Tau at a pH of 5.5 and no effect on the l-Lys- or Tau-insensitive component. In conclusion, Met transport across the apical membrane of Caco-2 cells is increased by low extracellular pH as the result of the stimulation of two transport systems functionally identified with systems L and B0,+for l-Met and with system B0,+for d-Met.
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Thwaites DT, Anderson CMH. Deciphering the mechanisms of intestinal imino (and amino) acid transport: The redemption of SLC36A1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:179-97. [PMID: 17123464 DOI: 10.1016/j.bbamem.2006.10.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Revised: 09/26/2006] [Accepted: 10/02/2006] [Indexed: 11/23/2022]
Abstract
The absorption of zwitterionic imino and amino acids, and related drugs, is an essential function of the small intestinal epithelium. This review focuses on the physiological roles of transporters recently identified at the molecular level, in particular SLC36A1, by identifying how they relate to the classical epithelial imino and amino acid transporters characterised in mammalian small intestine in the 1960s-1990s. SLC36A1 transports a number of D- and L-imino and amino acids, beta- and gamma-amino acids and orally-active neuromodulatory and antibacterial agents. SLC36A1 (or PAT1) functions as a proton-coupled imino and amino acid symporter in cooperation with the Na+/H+ exchanger NHE3 (SLC9A3) to produce the imino acid carrier identified in rat small intestine in the 1960s but subsequently ignored because of confusion with the IMINO transporter. However, it is the sodium/imino and amino acid cotransporter SLC6A20 which corresponds to the betaine carrier (identified in hamster, 1960s) and IMINO transporter (identified in rabbit and guinea pig, 1980s). This review summarises evidence for expression of SLC36A1 and SLC6A20 in human small intestine, highlights the differences in functional characteristics of the imino acid carrier and IMINO transporter, and explains the confusion surrounding these two distinct transport systems.
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Affiliation(s)
- David T Thwaites
- Epithelial Research Group, Institute for Cell and Molecular Biosciences, Faculty of Medical Sciences, Framlington Place, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
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Anderson CMH, Grenade DS, Boll M, Foltz M, Wake KA, Kennedy DJ, Munck LK, Miyauchi S, Taylor PM, Campbell FC, Munck BG, Daniel H, Ganapathy V, Thwaites DT. H+/amino acid transporter 1 (PAT1) is the imino acid carrier: An intestinal nutrient/drug transporter in human and rat. Gastroenterology 2004; 127:1410-22. [PMID: 15521011 DOI: 10.1053/j.gastro.2004.08.017] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
BACKGROUND AND AIMS Amino acid (and related drug) absorption across the human small intestinal wall is an essential intestinal function. Despite the revelation of a number of mammalian genomes, the molecular identity of the classic Na(+)-dependent imino acid transporter (identified functionally in the 1960s) remains elusive. The aims of this study were to determine whether the recently isolated complementary DNA hPAT1 (human proton-coupled amino acid transporter 1), or solute carrier SLC36A1, represents the imino acid carrier; the Na(+) -dependent imino acid transport function measured at the brush-border membrane of intact intestinal epithelia results from a close functional relationship between human proton-coupled amino acid transporter-1 and N(+) /H(+) exchanger 3 (NHE3). METHODS PAT1 function was measured in isolation ( Xenopus laevis oocytes) and in intact epithelia (Caco-2 cell monolayers and rat small intestine) by measurement of amino acid and/or H(+) influx. Tissue and membrane expression of PAT1 were determined by reverse-transcription polymerase chain reaction and immunohistochemistry. RESULTS PAT1-specific immunofluorescence was localized exclusively to the luminal membrane of Caco-2 cells and human and rat small intestine. The substrate specificity of hPAT1 is identical to that of the imino acid carrier. In intact epithelia, PAT1-mediated amino acid influx is reduced under conditions in which NHE3 is inactive. CONCLUSIONS The identification in intact epithelia of a cooperative functional relationship between PAT1 (H(+) /amino acid symport) and NHE3 (N(+) /H(+) exchange) explains the apparent Na + dependence of the imino acid carrier in studies with mammalian intestine. hPAT1 is the high-capacity imino acid carrier localized at the small intestinal luminal membrane that transports nutrients (imino/amino acids) and orally active neuromodulatory agents (used to treat affective disorders).
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Affiliation(s)
- Catriona M H Anderson
- Faculty of Medical Sciences, nUniversity of Newcastle Upon Tyne, Newcasttle Upon Tyne, UK
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Abstract
OBJECTIVE To measure nutrient absorption by the intestine during postnatal development of dogs. ANIMAL 110 Beagles ranging from neonatal to adult dogs. PROCEDURE Rates of absorption for sugars (glucose, galactose, and fructose), amino acids (aspartate, leucine, lysine, methionine, and proline), a dipeptide (glycyl-sarcosine), and linoleic acid by the proximal, mid, and distal regions of the small intestine were measured as functions of age and concentration (kinetics) by use of intact tissues and brush-border membrane vesicles. Absorption of octanoic acid by the proximal portion of the colon was measured in intact tissues. RESULTS Rates of carrier-mediated transport by intact tissues decreased from birth to adulthood for aldohexoses and most amino acids but not for fructose and aspartate. Kinetics and characteristics of absorption suggest that there were changes in the densities, types, and proportions of various carriers for sugars and amino acids. Saturable absorption of linoleic acid in the small intestine and octanoic acid in the proximal portion of the colon increased after weaning. CONCLUSIONS AND CLINICAL RELEVANCE Rates of absorption decreased between birth and adulthood for most nutrients. However, because of intestinal growth, absorption capacities of the entire small intestine remained constant for leucine and proline and increased for glucose, galactose, fructose, aspartate, and proline but were less than predicted from the increase in body weight. Although postnatal ontogeny of nutrient absorption was consistent with changes in the composition of the natural and commercial diets of growing dogs, rates of amino acid and peptide absorption were lower than expected.
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Affiliation(s)
- Randal K Buddington
- Department of Biological Sciences, College of Arts and Science, Mississippi State University, Mississippi State, MS 39762, USA
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Ngo LY, Patil SD, Unadkat JD. Ontogenic and longitudinal activity of Na(+)-nucleoside transporters in the human intestine. Am J Physiol Gastrointest Liver Physiol 2001; 280:G475-81. [PMID: 11171631 DOI: 10.1152/ajpgi.2001.280.3.g475] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The objectives of our study were to identify the types of nucleoside transporters present in the human fetal small intestine and to characterize their developmental activity, longitudinal distribution, and transport kinetics compared with those present in the adult intestine. Nucleoside uptake by intestinal brush-border membrane vesicles was measured by an inhibitor-stop rapid filtration technique. Only the purine-specific (N1; hCNT2) and the pyrimidine-specific (N2; hCNT1) Na(+)-dependent nucleoside transporters were found to be present on the brush-border membranes of the enterocytes along the entire length of the fetal and adult small intestines. The activity of these transporters was higher in the proximal than in the distal small intestine. Both the N1 and N2 transporters found in the fetal intestine shared similar kinetic properties (Michaelis-Menten constant and Na(+)-nucleoside stoichiometry) to those in the adult intestine. During the period of rapid morphogenesis (11-15 wk gestation), no temporal differences were apparent in the activity of the N1 and N2 transporters in the fetal small intestine. These findings have implications for the absorption of drugs from the amniotic fluid by the fetus after maternal drug administration of nucleoside drugs such as the antivirals zidovudine and didanosine.
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Affiliation(s)
- L Y Ngo
- Department of Pharmaceutics, University of Washington, Seattle, Washington 98195, USA
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Berger V, Larondelle Y, Trouet A, Schneider YJ. Transport mechanisms of the large neutral amino acid L-phenylalanine in the human intestinal epithelial caco-2 cell line. J Nutr 2000; 130:2780-8. [PMID: 11053521 DOI: 10.1093/jn/130.11.2780] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The transepithelial transport and the intracellular accumulation of the large neutral amino acid L-phenylalanine (L-Phe) were studied in monolayers of Caco-2 cells, cultivated in a bicameral insert system, to characterize the mechanisms involved in the absorption of this essential amino acid by the human intestinal mucosa. In our model, L-Phe was transported selectively in the apical (AP)-to-basolateral (BL) direction. AP-to-BL transport of L-Phe was temperature dependent and Na(+) independent, increased in the absence of protein synthesis and showed competition with large neutral and cationic amino acids. By contrast, transport in the BL-to-AP direction mainly resulted from passive movement (probably paracellular passage and transcellular diffusion). L-Phe accumulation into Caco-2 cells was higher from the BL pole than from the AP pole and characterized by the incorporation of most of the accumulated molecules into newly synthesized proteins. In addition, L-Phe accumulation was Na(+) dependent from both poles, whereas only accumulation from the AP pole was sensitive to inhibition by both large neutral and cationic amino acids. These results suggest that the processes involved in AP-to-BL transport and AP accumulation of this amino acid are very different from those involved in BL-to-AP transport and BL accumulation.
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Affiliation(s)
- V Berger
- Laboratoire de Biochimie Cellulaire, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
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Berger V, De Bremaeker N, Larondelle Y, Trouet A, Schneider YJ. Transport mechanisms of the imino acid L-proline in the human intestinal epithelial caco-2 cell line. J Nutr 2000; 130:2772-9. [PMID: 11053520 DOI: 10.1093/jn/130.11.2772] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The intestinal transport of L-proline (L-Pro) has been investigated in various animal species with the use of different tissue preparations. Because major qualitative differences have been observed among the species, it is difficult to extent the results obtained with animal models to humans. In addition, studies on human tissue are lacking because of difficulties in obtaining material for experiments. To characterize the mechanisms involved in the intestinal absorption of L-Pro in humans, the transport of this nonessential imino acid was studied in monolayers of human intestinal Caco-2 cells that were cultivated on microporous membranes. In this model, L-Pro was transported selectively in the apical (AP)-to-basolateral (BL) direction. This transport was significantly reduced by metabolic inhibitors and by an incubation at 4 degrees C; it was Na(+) dependent and showed competition with (methylamino)-alpha-isobutyric acid and L-hydroxyproline. By contrast, transport in the BL-to-AP direction resulted to a large extent from passive movement (paracellular passage and transcellular diffusion). L-Pro accumulation by Caco-2 cells was significantly greater from the AP pole than from the BL pole. About 30-50% of the accumulated molecules were incorporated into newly synthesized proteins in a process inhibited by cycloheximide, whereas the remainder were extensively metabolized into non-amino acid compounds. L-Pro accumulations from the AP and BL poles were both Na(+) dependent, but they exhibited different characteristics. AP accumulation was inhibited by competition with (methylamino)-alpha-isobutyric acid, L-hydroxyproline and, to a lesser extent, D-Pro, whereas BL accumulation was inhibited by competition with L-hydroxyproline, (methylamino)-alpha-isobutyric acid, alpha-aminoisobutyric acid, L-histidine and small neutral amino acids. The results indicate that AP-to-BL transport and AP accumulation of L-Pro exhibited very different characteristics than BL-to-AP transport and BL accumulation.
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Affiliation(s)
- V Berger
- Laboratoire de Biochimie Cellulaire, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
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Abstract
Considerable progress has been made over the last decade in the understanding of mechanisms responsible for the ontogenetic changes of mammalian intestine. This review presents the current knowledge about the development of intestinal transport function in the context of intestinal mucosa ontogeny. The review predominantly focuses on signals that trigger and/or modulate the developmental changes of intestinal transport. After an overview of the proliferation and differentiation of intestinal mucosa, data about the bidirectional traffic (absorption and secretion) across the developing intestinal epithelium are presented. The largest part of the review is devoted to the description of developmental patterns concerning the absorption of nutrients, ions, water, vitamins, trace elements, and milk-borne biologically active substances. Furthermore, the review examines the development of intestinal secretion that has a variety of functions including maintenance of the fluidity of the intestinal content, lubrication of mucosal surface, and mucosal protection. The age-dependent shifts of absorption and secretion are the subject of integrated regulatory mechanisms, and hence, the input of hormonal, nervous, immune, and dietary signals is reviewed. Finally, the utilization of energy for transport processes in the developing intestine is highlighted, and the interactions between various sources of energy are discussed. The review ends with suggestions concerning possible directions of future research.
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Affiliation(s)
- J Pácha
- Institute of Physiology, Czech Academy of Sciences, Prague, Czech Republic.
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Thiesen A, Wild G, Keelan M, Clandinin MT, McBurney M, Aerde JV, Thomson ABR. Ontogeny of intestinal nutrient transport. Can J Physiol Pharmacol 2000. [DOI: 10.1139/y00-018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be life-saving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.Key words: absorption, adaptation, diet, peptides.
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Hatanaka T, Nabuchi Y, Ushio H. Na(+)-dependent and Na(+)-independent transport of L-arginine and L-alanine across dog intestinal brush border membrane vesicles. Comp Biochem Physiol B Biochem Mol Biol 1999; 123:105-13. [PMID: 10425715 DOI: 10.1016/s0305-0491(99)00049-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
We prepared intestinal brush border membrane vesicles (BBMVs) from beagle dogs fed a commercial diet (protein content: 24-26%), and investigated the characteristics of transport for basic and neutral amino acids across the intestinal BBMVs. To determined the kinetic parameters for L-arginine and L-alanine uptake, their total uptake was resolved into three routes: (1) Na(+)-dependent carrier-mediated transport; (2) Na(+)-independent carrier-mediated transport; and (3) simple diffusion. We could observe subtle, but clear-cut, Na(+)-dependent basic amino acid transport for the first time among studies with intestinal BBMVs prepared from mammals fed a normal diet. The Na(+)-dependent system for L-arginine transport can be best characterized as 'low affinity, low capacity', in contrast to that for L-alanine transport, which is 'low affinity, high capacity'. Maximal velocities of the Na(+)-dependent carrier-mediated transport are estimated to be higher for both L-arginine and L-alanine in dog intestinal BBMVs than in rabbit intestinal BBMVs reported previously. These results suggest that food habit of mammals is an important factor to decide the characteristic of system B0,+, a Na(+)-dependent carrier-mediated transport system common to basic and neutral amino acids across intestinal brush border membranes, as is protein content of the diet.
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Affiliation(s)
- T Hatanaka
- Fuji Gotemba Research Laboratory, Chugai Pharmaceutical Co., Ltd., Shizuoka, Japan.
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16
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Abstract
A combination of approaches has begun to elucidate the mechanisms of gastrointestinal development. This review describes progress over the last 20 years in understanding human gastrointestinal development, including data from both human and experimental animal studies that address molecular mechanisms. Rapid progress is being made in the identification of genes regulating gastrointestinal development. Genes directing initial formation of the endoderm as well as organ-specific patterning are beginning to be identified. Signaling pathways regulating the overall right-left asymmetry of the gastrointestinal tract and epithelial-mesenchymal interactions are being clarified. In searching for extrinsic developmental regulators, numerous candidate trophic factors have been proposed, but compelling evidence remains elusive. A critical gene that initiates pancreas development has been identified, as well as a number of genes regulating liver, stomach, and intestinal development. Mutations in genes affecting neural crest cell migration have been shown to give rise to Hirschsprung's disease. Considerable progress has been achieved in understanding specific phenomena, such as the transcription factors regulating expression of sucrase-isomaltase and fatty acid-binding protein. The challenge for the future is to integrate these data into a more complete understanding of the physiology of gastrointestinal development.
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Affiliation(s)
- R K Montgomery
- Division of Pediatric Gastroenterology and Nutrition, The Floating Hospital for Children at New England Medical Center, Boston, MA 02111-1533, USA
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17
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Soriano-García JF, Torras-Llort M, Ferrer R, Moreto M. Multiple pathways for L-methionine transport in brush-border membrane vesicles from chicken jejunum. J Physiol 1998; 509 ( Pt 2):527-39. [PMID: 9575301 PMCID: PMC2230979 DOI: 10.1111/j.1469-7793.1998.527bn.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
1. The intestinal transport of L-methionine has been investigated in brush-border membrane vesicles isolated from the jejunum of 6-week-old chickens. L-Methionine influx is mediated by passive diffusion and by Na+-dependent and Na+-independent carrier-mediated mechanisms. 2. In the absence of Na+, cis-inhibition experiments with neutral and cationic amino acids indicate that two transport components are involved in L-methionine influx: one sensitive to L-lysine and the other sensitive to 2-aminobicyclo[2.2. 1]heptane-2-carboxylic acid (BCH). The L-lysine-sensitive flux is strongly inhibited by L-phenylalanine and can be broken down into two pathways, one sensitive to N-ethylmaleimide (NEM) and the other to L-glutamine and L-cystine. 3. The kinetics of L-methionine influx in Na+-free conditions is described by a model involving three transport systems, here called a, b and c: systems a and b are able to interact with cationic amino acids but differ in their kinetic characteristics (system a: Km = 2.2 +/- 0.3 microM and Vmax = 0.13 +/- 0.005 pmol (mg protein)-1 (2 s)-1; system b: Km = 3.0 +/- 0.3 mM and Vmax = 465 +/- 4.3 pmol (mg protein)-1 (2 s)-1); system c is specific for neutral amino acids, has a Km of 1.29 +/- 0.08 mM and a Vmax of 229 +/- 5.0 pmol (mg protein)-1 (2 s)-1 and is sensitive to BCH inhibition. 4. The Na+-dependent component can be inhibited by BCH and L-phenylalanine but cannot interact either with cationic amino acids or with alpha-(methylamino)isobutyrate (MeAIB). 5. The kinetic analysis of L-methionine influx under a Na+ gradient confirms the activity of the above described transport systems a and b. System a is not affected by the presence of Na+ while system b shows a 3-fold decrease in the Michaelis constant and a 1.4-fold increase in Vmax. In the presence of Na+, the BCH-sensitive component can be subdivided into two pathways: one corresponds to system c and the other is Na+ dependent and has a Km of 0.64 +/- 0. 013 mM and a Vmax of 391 +/- 2.3 pmol (mg protein)-1 (2 s)-1. 6. It is concluded that L-methionine is transported in the chicken jejunum by four transport systems, one with functional characteristics similar to those of system bo, + (system a); a second (system b) similar to system y+, which we suggest naming y+m to account for its high Vmax for L-methionine transport in the absence of Na+; a third (system c) which is Na+ independent and has similar properties to system L; and a fourth showing Na+ dependence and tentatively identified with system B.
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Affiliation(s)
- J F Soriano-García
- Departament de Fisiologia-Divisio IV, Facultat de Farmàcia, Universitat de Barcelona, E-08028 Barcelona, Spain
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18
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Munck LK. Comparative aspects of chloride-dependent amino acid transport across the brush-border membrane of mammalian small intestine. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART A, PHYSIOLOGY 1997; 118:229-31. [PMID: 9366049 DOI: 10.1016/s0300-9629(97)00072-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Chloride-dependent amino acid transport has been described in several tissues. This article briefly reviews the evidence of cotransport of chloride and amino acids across the brush-border membrane of rabbit distal ileum. On the basis of amino acid carriers described in the rabbit and the surveys of chloride-dependence reported, a comparison of amino acid carriers in the mammalian small intestine is performed. Additional characteristics of the carriers in the different species are included in the discussion when necessary. From this comparison the rabbit distal ileum and the pig small intestine emerge as the best models of amino acid transport in the human small intestine.
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Affiliation(s)
- L K Munck
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark
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19
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Hoekstra JH, van den Aker JH. Facilitating effect of amino acids on fructose and sorbitol absorption in children. J Pediatr Gastroenterol Nutr 1996; 23:118-24. [PMID: 8856576 DOI: 10.1097/00005176-199608000-00004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The facilitating effect of glucose on free fructose absorption has been suggested to be due to a sucrase-related transport mechanism. In contrast, the conditions influencing the absorption of sorbitol have hardly been investigated. As amino acids promote transcellular water flow, we investigated their effects on the absorption of fructose and sorbitol. We studied 15 healthy children using breath hydrogen tests following the ingestion of fructose and sorbitol, alone and in combination with glucose or amino acids. Similarly, the effect of acarbose pretreatment on sucrose and fructose-glucose absorption was investigated. The inhibition of sucrase isomaltase by acarbose impedes the absorption of sucrose but not of the fructose-glucose mixture. Fructose absorption is enhanced by glucose and by the amino acids L-alanine, L-glutamine, L-phenylalanine, and L-proline. Similarly, the absorption of sorbitol is facilitated by glucose and L-alanine. These results are not in concordance with a sucrase-related fructose-transport system and suggest another mechanism for glucose-induced enhancement of fructose (and sorbitol) absorption. We hypothesize that the absorption of fructose and sorbitol may be stimulated by the increased water flux induced by active absorption of glucose as well as amino acids.
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Affiliation(s)
- J H Hoekstra
- Division of Paediatrics, Bosch Medicentrum, 's-Hertogenbosch, The Netherlands
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20
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Buddington RK, Malo C. Intestinal brush-border membrane enzyme activities and transport functions during prenatal development of pigs. J Pediatr Gastroenterol Nutr 1996; 23:51-64. [PMID: 8811524 DOI: 10.1097/00005176-199607000-00010] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Enzyme activities and rates of leucine and glucose uptake were measured using brush-border membrane vesicles prepared from the small intestine of 7-, 8-, 10-, and 12-week fetal (43, 49, 61, and 74% of gestation) and unsuckled, neonatal pigs. Lactase was detected in 7-week fetuses, with a large increase in activity between 10 weeks of gestation and birth. gamma-Glutamyltranspeptidase activity was stable throughout gestation, whereas sucrase activity was not detected. Active L-leucine uptake was already present at 7 weeks of gestation, with an increasing distal-to-proximal gradient observed at birth. D-glucose uptake was low at 7 weeks, but by 8 weeks it exhibited a typical overshoot phenomenon and established a decreasing proximal-to-distal gradient by 12 weeks. D-glucose uptake at all ages was directly related to incubation temperature, but less so for 7- and 10-week fetuses. By 12 weeks strict Na(+)-dependency of D-glucose uptake was observed along the entire length of the small intestine. Kinetic analysis of Na(+)-D-glucose cotransport showed a shift from the presence of both high- and low-affinity systems at 8 weeks of gestation to a single high-affinity Michaelian component at birth. In light of similarities with human fetuses, the pig may be a valuable model for studying development of intestinal transport during gestation, particularly during the final trimester, when availability of human tissue is limited.
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Affiliation(s)
- R K Buddington
- Department of Biological Sciences, Mississippi State University, Mississippi State 39762-5759, USA
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21
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Munck LK. Chloride-dependent amino acid transport in the small intestine: occurrence and significance. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1241:195-213. [PMID: 7640296 DOI: 10.1016/0304-4157(95)00005-c] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The unidirectional influx of amino acids, D-glucose and ions across the brush-border membrane of the small intestine of different species has been measured in vitro with emphasis on characterization of topographic and species differences and on chloride dependence. The regional differences in transport along the small intestine are outlined and shown to be caused by variation in transport capacity, while the apparent affinity constants are unchanged. Rabbit small intestine is unique by exhibiting maximal rates of transport in the distal ileum and a very steep decline in the oral direction from where tissues are normally harvested for preparation of brush-border membrane vesicles. Transport in the guinea pig and rat is much more constant throughout the small intestine. Since the capacity of nutrient carriers is regulated by their substrates it is possible that bacterial breakdown of peptides and proteins in rabbit distal ileum increases the concentration of amino acids leading to an upregulation of the carriers. Chloride dependence is a characteristics of the carrier rather than the transported amino acid, and is used to improve the classification of amino acid carriers in rabbit small intestine. In this species the imino acid carrier, the beta-amino acid carrier, and the beta-alanine carrier, which should be renamed the B0,+ carrier, are chloride-dependent. The steady-state mucosal uptake of classical substrates for these carriers in biopsies from the human duodenum is also chloride-dependent. The carrier of beta-amino acids emerges as ubiquitous and chloride-dependent, and evidence of cotransport with both sodium and chloride is reviewed. A sodium:chloride:2-methyl-aminoisobutyric acid coupling stoichiometry of approx. 2:1:1 is suggested by ion activation studies. Direct measurements of coupled ion fluxes in rabbit distal ileum confirm that sodium, chloride and 2-methyl-aminoisobutyric acid are cotransported on the imino acid carrier with an identical influx stoichiometry. Control experiments and reference to the literature on the electrophysiology of the small intestine exclude alterations of the membrane potential as a feasible explanation of the chloride dependence. Thus, it is concluded that chloride is cotransported with both sodium and 2-methyl-aminoisobutyric acid across the brush-border membrane of rabbit distal ileum.
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Affiliation(s)
- L K Munck
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark
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22
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Pan M, Stevens BR. Differentiation- and protein kinase C-dependent regulation of alanine transport via system B. J Biol Chem 1995; 270:3582-7. [PMID: 7876094 DOI: 10.1074/jbc.270.8.3582] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The regulation of sodium-dependent L-alanine transport is described for the first time in intestinal cells. Substrate analogue inhibition patterns and Dixon analyses indicated that uptake occurred via transport system B, an epithelial cell variant of systems B0,+ and ASC. System B served > 95% of the Na(+)-dependent alanine uptake in both undifferentiated (2 days postpassaging) and differentiated (> 9 days postpassaging) states of the human Caco-2 cultured intestinal cell line. (Methylamino)isobutyric acid-inhibitable system A transport accounted for < 5% of total alanine uptake. System B activity was greater in undifferentiated cells compared with the differentiated state, and activity at any differentiation state was stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA). The maximal stimulation, determined by TPA dose-response/exposure time data, was attributable to a change in cell transport capacity (Vmax), with Km unaffected. The Vmax of system B was greater in 2-day-old cells (2.79 +/- 0.21 nmol min-1 mg of protein-1; Km = 164 +/- 26 microM alanine), decreasing to Vmax = 0.51 +/- 0.03 nmol min-1 mg of protein-1 (Km = 159 +/- 14 microM) in 9-day-old cells. Regardless of differentiation status, the sodium-activation Hill coefficient was 1.06 +/- 0.10, and the alanine passive diffusion permeability coefficient was 0.53 +/- 0.08 microliter min-1 mg of protein-1. Phorbol ester up-regulated the Vmax of system B in 2-day-old cells to Vmax = 6.32 +/- 0.37 nmol min-1 mg of protein-1 (Km = 169 +/- 18 microM), and in 9-day-old cells to Vmax = 1.42 +/- 0.05 nmole min-1 mg of protein-1 (Km = 180 +/- 10 microM). Phorbol ester stimulation of transport occurred after at least 6 h of continual exposure, and was blocked by the protein kinase C inhibitors chelerythrine or photoactivated calphostin C. Protein synthesis inhibitors cycloheximide and actinomycin D each blocked the phorbol ester up-regulation of system B activity. It is concluded that Caco-2 cells regulate carrier-mediated sodium-dependent transport of L-alanine by changing the membrane capacity to transport alanine via system B and that this regulation involves de novo protein synthesis under the control of protein kinase C.
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Affiliation(s)
- M Pan
- Department of Physiology, College of Medicine, University of Florida, Gainesville 32610
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23
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Abstract
1. The proposal that rabbit small intestine possesses a separate, sodium-dependent carrier of phenylalanine has been examined by measurements of the unidirectional influx of amino acids across the brush-border membrane of the intact epithelium of the rabbit small intestine. 2. We demonstrate that, like alanine, glycine and leucine, phenylalanine shares sodium-dependent as well as sodium-independent transport with lysine. 3. Using the distal ileum we applied the A (phenylalanine)-B (leucine)-C (alanine) test on the sodium-dependent, lysine-resistant transport of phenylalanine. For phenylalanine, K1/2 (concentration required for half-maximal transport) was 3.1 +/- 0.2 mM (n = 7) and Ki (inhibitor constant) against leucine transport was 3.1 +/- 0.2 mM (n = 4). For leucine, K1/2 was 1.1 +/- 0.1 mM (n = 4) and Ki against transport of phenylalanine was 1.1 +/- 0.1 mM (n = 4). For alanine, K1/2 was 12.6 +/- 1.1 mM (n = 3), Ki against phenylalanine was 13.1 +/- 1.8 mM (n = 4) and Ki against leucine was 11.0 +/- 0.4 mM (n = 4). 4. Using the jejunum we applied the A (phenylalanine)-B (alanine)-C (methionine) test on the lysine-resistant, sodium-dependent transport of phenylalanine. For phenylalanine, K1/2 was 4.7 +/- 0.2 mM (n = 7) and Ki against alanine was 4.8 +/- 0.2 mM (n = 4). For alanine, K1/2 was 15.6 +/- 0.8 mM (n = 7) and Ki against phenylalanine was 18.1 +/- 0.9 mM (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- B G Munck
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark
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24
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Dibner JJ, Atwell CA, Ivey FJ. Effect of heat stress on 2-hydroxy-4-(methylthio)butanoic acid and DL-methionine absorption measured in vitro. Poult Sci 1992; 71:1900-10. [PMID: 1437977 DOI: 10.3382/ps.0711900] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The objective of the present experiments was to determine the biochemical basis for preliminary chick performance data, which indicate an ameliorative effect of 2-hydroxy-4-(methylthio)butanoic acid (HMB) when compared with DL-methionine (DLM) fed during hot conditions. In vitro passage of HMB or DLM across intact segments of small intestine from either control (thermoneutral, TN) or heat-stressed (HS) birds was used as a model for intestinal absorption. For DLM placed in the lumen, appearance in the outside buffer was reduced when using intestine from HS birds compared with tissue from TN birds. In contrast, the appearance of HMB in the outside buffer was greater using HS intestine, resulting in a substrate by environment interaction (P < .01). Slices of everted small intestine from TN and HS birds were used to study epithelial uptake of methyl labeled 14C-DLM by three transport pathways: diffusion, carrier-specific energy- and sodium-independent uptake (ESI), and carrier-specific energy- and sodium-dependent uptake (ESD). Correcting for extracellular volume, total epithelial uptake of 14C-DLM (diffusion plus ESI plus ESD) was reduced by 34% in HS intestine (P < .05). Energy-dependent uptake was observed to decrease by 87% in HS (P < .05). Energy-independent uptake was increased (136%, HS versus TN, P < .05), but not enough to compensate for the decrease in ESD uptake. Intestinal transport systems for glucose and leucine were also observed to change during HS, suggesting a role for cellular transport changes in the performance reduction associated with HS.
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Affiliation(s)
- J J Dibner
- Novus International, Inc., Chesterfield, Missouri 63198
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25
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Nicklin PL, Irwin WJ, Hassan IF, Mackay M. Proline uptake by monolayers of human intestinal absorptive (Caco-2) cells in vitro. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1104:283-92. [PMID: 1547265 DOI: 10.1016/0005-2736(92)90042-k] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Monolayers of the Caco-2 human intestinal cell line exhibit active and passive uptake systems for the imino acid L-proline. The active transport component is saturable and it is responsible for about two thirds of the observed flux over the nanomolar concentration range, at 37 degrees C and pH 7.4. In contrast to L-phenylalanine, specific L-proline uptake has a high degree of sodium dependency and the efficiency of the carrier system is significantly reduced when protein synthesis (cycloheximide), Na+/K(+)-ATPase (ouabain) or cellular metabolism (sodium azide) are inhibited. The expression of the L-proline carrier by Caco-2 cells was under some degree of nutritional control. Glucose deficiency, over the time scale of the experiment, had no effect. The temperature-dependence of the specific uptake process followed the Arrhenius model with an apparent activation energy of 93.5 kJ nmol-1. This pathway also displayed Michaelis-Menten concentration-dependence with a Ksdm of 5.28 mM and a maximal transport flux (Jsdmax) of 835 pmol min-1 (10(6) cells)-1. Although the passive component was unchanged, the pH of the donor phase exerted a profound effect on the active carrier component. Within the physiological pH range a local maximum efficiency was found at pH 7.4 but dramatic increases were noted as pH 5.0 was approached. In competition studies, with 100-fold excess of a second amino acid, strong inhibition of uptake was found with alpha-aminoisobutyric acid, L-alanine and L-serine whereas moderate inhibition was observed with glycine, D-proline and gamma-aminoisobutyric acid. Aromatic and branched amino acids showed weak (L-valine) or no interaction (L-phenylalanine, L-leucine) with the carrier system. These data indicate that the carrier system for the uptake of L-proline has many features in common with the A system for amino acid transport.
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Affiliation(s)
- P L Nicklin
- Pharmaceutical Sciences Institute, Aston University, Birmingham, UK
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