scholarly journals Intracellular Na+ and the control of amino acid fluxes in the integumental epithelium of a marine bivalve

1989 ◽  
Vol 142 (1) ◽  
pp. 293-310
Author(s):  
S. H. Wright ◽  
D. A. Moon ◽  
A. L. Silva
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Sea Water ◽  
Gill Tissue ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Marine Bivalve ◽  
Chemical Gradients ◽  
Influx Pathways ◽  
Taurine Efflux

The accumulation of amino acids from sea water into the integumental epithelium of the bivalve gill can occur against chemical gradients in excess of 10(6) to 1. The energy to drive this transport has been proposed to come from the inwardly directed Na+ electrochemical gradient. The present study examined the influence of intracellular and extracellular [Na+] on influx and efflux of amino acids in gill tissue from the mussel, Mytilus californianus. Influx of alanine was inhibited by more than 90% when external [Na+] was reduced from 425 to 2 mmol l-1, and by 85% when intracellular [Na+] was increased from approximately 11 to approximately 100 mmol l-1 (by means of a 30-min exposure to the ionophore, nigericin). Efflux of taurine and alanine from gill tissue into normal-Na+ sea water was very low (less than 5% of the Jmax of the carrier-mediated influx pathways). Reducing the external Na+ from 425 to 2 mmol l-1 increased taurine efflux by only 20%. Raising cell [Na+] to approximately 100 mmol l-1 increased taurine efflux 2.7-fold; further increases in cell [Na+] increased taurine efflux another 7.5-fold. These data, in conjunction with results from earlier studies, suggest that activation of integumental amino acid transporters requires an interaction of multiple sodium ions with binding sites of low affinity for this ion. This set of characteristics results in transport systems that are well-adapted for the net accumulation of amino acids from sea water.

Placental amino acid transport

1995 ◽  
Vol 268 (6) ◽  
pp. C1321-C1331 ◽  
Author(s):  
A. J. Moe
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Human Placenta ◽  
Amino Acid Transport ◽  
Single Layer ◽  
Maternal Blood ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Principal Mechanism

Normal fetal growth and development depend on a continuous supply of amino acids from the mother to the fetus. The placenta is responsible for the transfer of amino acids between the two circulations. The human placenta is hemomonochorial, meaning that the maternal and fetal circulations are separated by a single layer of polarized epithelium called the syncytiotrophoblast, which is in direct contact with maternal blood. Transport proteins located in the microvillous and basal membranes of the syncytiotrophoblast are the principal mechanism for transfer from maternal blood to fetal blood. Knowledge of the function and regulation of syncytiotrophoblast amino acid transporters is of great importance in understanding the mechanism of placental transport and potentially improving fetal and newborn outcomes. The development of methods for the isolation of microvillous and basal membrane vesicles from human placenta over the past two decades has contributed greatly to this understanding. Now a primary cultured trophoblast model is available to study amino acid transport and regulation as the cells differentiate. The types of amino acid transporters and their distribution between the syncytiotrophoblast microvillous and basal membranes are somewhat unique compared with other polarized epithelia. These differences may reflect the unusual circumstance of this epithelium that is exposed to blood on both sides. The current state of knowledge as to the types of transport systems present in syncytiotrophoblast, their regulation, and the effects of maternal consumption of drugs on transport are discussed.

scholarly journals Apical Membrane Permeability of Mytilus Gill: Influence of Ultrastructure, Salinity and Competitive Inhibitors on Amino Acid Fluxes

1987 ◽  
Vol 129 (1) ◽  
pp. 205-230
Author(s):  
STEPHEN H. WRIGHT ◽  
TIMOTHY W. SECOMB ◽  
TIMOTHY J. BRADLEY
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Apical Membrane ◽  
Sea Water ◽  
Gill Tissue ◽  
Permeability Barrier ◽  
Acid Uptake ◽  
Passive Permeability ◽  
Membrane Area ◽  
Kinetics Of

The apical membrane of gill integumental cells from the mussels Mytilus edulis and M. californianus serves as a permeability barrier separating sea water from a cytoplasm rich in amino acids and other small organic molecules. Morphometric analysis of transmission electronmicrographs indicates that the membrane area of these cells is increased between 10- and 18-fold by the presence of a microvillous brush border. The microvilli do not appear to influence the kinetics of solute transport across the cell apex, as determined using a mathematical model of the relationship between membrane structure and the kinetics of transport. Rates of amino acid loss from the integument were low, and estimates of the upper limit of the passive permeability of the apical membrane to amino acids ranged from 0.5 to 10×10−10cm s−1. Abrupt exposure of intact mussels or isolated gill tissue to 60% sea water (19% salinity) resulted in a transient, 40- to 80-fold increase in the rate of loss of all amino acids from integumental tissues. Upon exposure to full-strength sea water, efflux rates returned to near control values. Exposure to 60% sea water also inhibited the carrier-mediated accumulation of amino acid: uptake of 0.5 μmol1−1 [14C]alanine and [14C]taurine was reduced by 80% compared to control uptake in 100% sea water. This inhibition was not adequate to account for the increase in net efflux of taurine from gill tissue into 60% artificial sea water (ASW), though the inhibition of alanine uptake may have contributed significantly to the increased loss of this amino acid. Efflux of discrete structural classes of amino acid occurred when integumental tissues were exposed to 50 μmoll−1 concentrations of structurally related analogues. It is concluded that the apical membrane of gill cells has a very low passive permeability to amino acids, and that the overall permeability of the gill can be increased in a reversible fashion by exposure to reduced salinity or to high external concentrations of amino acid.

Simultaneous determination of net uptake of 16 amino acids by a marine bivalve

1983 ◽  
Vol 244 (6) ◽  
pp. R832-R838 ◽  
Author(s):  
D. T. Manahan ◽  
S. H. Wright ◽  
G. C. Stephens
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
High Performance ◽  
Amino Acid Uptake ◽  
Marine Bivalve ◽  
Acid Uptake ◽  
Chemical Gradients ◽  
Net Uptake ◽  
Ambient Concentrations ◽  
Net Flux

High-performance liquid chromatography was used to measure the simultaneous transport of 16 amino acids from seawater into the mussel Mytilus edulis. All the substrates, including representative neutral, basic, and acidic amino acids, were accumulated from ambient concentrations as low as 5 nM. Influx of four radioactively labeled amino acids was compared with their net flux. In each case the influx of the 14C-labeled substrate, determined from the removal of isotope from test solutions, accurately represented the net flux of that substrate as measured by direct chemical analysis. Ammonia was the only compound observed to be routinely lost from these animals. Rates of uptake of individual amino acids, each at concentrations of 10 nM, ranged from 2.4 to 7.0 nmol . g dry flesh wt-1 . min-1. The studies show that M. edulis is capable of a net uptake of dissolved amino acid from the very low concentrations characteristic of seawater. Moreover, net accumulation can occur against chemical gradients calculated to be in excess of one million to one. The rates of amino acid uptake may contribute significantly to the animals' energy requirements.

scholarly journals Transepithelial flux of early and advanced glycation compounds across Caco-2 cell monolayers and their interaction with intestinal amino acid and peptide transport systems

2006 ◽  
Vol 95 (6) ◽  
pp. 1221-1228 ◽  
Author(s):  
Simone Grunwald ◽  
René Krause ◽  
Mandy Bruch ◽  
Thomas Henle ◽  
Matthias Brandsch
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Peptide Transport ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Advanced Glycation ◽  
Simple Diffusion ◽  
Cell Monolayers ◽  
Maillard Products ◽  
Space Marker

Maillard products arise from condensation reactions between amino acids or proteins with reducing sugars during food processing. As ubiquitous components of human food, these early or advanced glycation products may be subject to intestinal absorption. The present study was performed to investigate the intestinal uptake of Maillard products and to determine whether they are substrates for peptide and amino acid transporters expressed at the apical membrane of Caco-2 cells. At a concentration of 10mm, Nɛ-(carboxymethyl)-L-lysine, Nα-hippuryl-Nɛ-(1-deoxy-d-fructosyl)-l-lysine,Nα-hippuryl-Nɛ-(carboxymethyl)-L-lysine and Nɛ-(1-deoxy-d-fructosyl)-l-lysine inhibited the [14C]glycylsarcosine uptake mediated by the H+–peptide co-transporter PEPT1 by 13 to 45%.For Nɛ-(1-deoxy-d-fructosyl)-l-lysine, an inhibitory constant of 8·7mm was determined, reflecting a low affinity to PEPT1 in comparison with natural dipeptides. Uptake of l-[3H]lysine was weakly affected by Nɛ-(carboxymethyl)-L-lysine, Nα-hippuryl-l-lysine and Nα-hippuryl-Nɛ-(carboxymethyl)-L-lysine but strongly inhibited by Nɛ-(1-deoxy-d-fructosyl)-l-lysine (81%). None of the Maillard products was able to inhibit the uptake of l-[3H]leucine by more than 15%. We also studied the transepithelial flux of Maillard productsacross Caco-2 cell monolayers cultured on permeable filters. The flux rates of Maillard products ranged from 0·01 to 0·3%/cm2 per h and were shown to be muchlower than those of carrier substrates such as glycylsarcosine, l-proline and the space marker 14C]mannitol. We conclude that the Maillard products investigated in the present study are neither transported by PEPT1 nor by carriers for neutral amino acids. The low transepithelial flux measured for these compounds most probably occurs by simple diffusion.

Mechanisms of integumental amino acid transport in marine bivalves

1989 ◽  
Vol 257 (3) ◽  
pp. R473-R483 ◽  
Author(s):  
S. H. Wright ◽  
A. M. Pajor
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Gill Tissue ◽  
Marine Bivalve ◽  
Animal Cells ◽  
Marine Bivalves ◽  
Near Shore ◽  
Ambient Concentrations ◽  
High Concentrations ◽  
Nutritional Strategies

The marine bivalve integument accumulates amino acids from seawater at rates that can significantly supplement other nutritional strategies. Reviewed here are studies that used both intact bivalve gill tissue and membranes isolated from gills to examine the mechanism of integumental transport. The evidence supports a model for secondary active transport in which an inward flux of Na+ down its electrochemical gradient provides the energy to support uptake of amino acids. Indeed, the Na+-cotransport paradigm appears to be a ubiquitous strategy by which animal cells energize uphill transport of organic solutes. What appears to distinguish integumental processes from others are the conditions under which they must routinely work: exposed to ambient concentrations of substrate of less than 1 microM and to cytoplasmic concentrations that exceed 0.1 M, transport of amino acid occurs against gradients that can exceed 10(6) to 1! Somewhat paradoxically, these transporters, which are characterized by an extremely high affinity for amino acid (Kt values of congruent to 5 microM), work so well because they have a low affinity for Na+; low cytoplasmic Na+ concentrations prevent the system from acting as an avenue for efflux, whereas the very high concentrations of Na+ in seawater are adequate to fully activate the influx mode of operation. The combination of these kinetic characteristics results in a class of transporters that makes efficient use of the scarce nutritional resource represented by dissolved organic material in near-shore waters.

scholarly journals The Proposed Neurotoxin β-N-Methylamino-l-Alanine (BMAA) Is Taken up through Amino-Acid Transport Systems in the Cyanobacterium Anabaena PCC 7120

Toxins ◽  
2020 ◽  
Vol 12 (8) ◽  
pp. 518
Author(s):  
Zi-Qian Wang ◽  
Suqin Wang ◽  
Ju-Yuan Zhang ◽  
Gui-Ming Lin ◽  
Nanqin Gan ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Transport Pathways ◽  
Anabaena Pcc 7120 ◽  
Cyanobacterium Anabaena ◽  
Pcc 7120

Produced by cyanobacteria and some plants, BMAA is considered as an important environmental factor in the occurrence of some neurodegenerative diseases. Neither the underlying mechanism of its toxicity, nor its biosynthetic or metabolic pathway in cyanobacteria is understood. Interestingly, BMAA is found to be toxic to some cyanobacteria, making it possible to dissect the mechanism of BMAA metabolism by genetic approaches using these organisms. In this study, we used the cyanobacterium Anabaena PCC 7120 to isolate BMAA-resistant mutants. Following genomic sequencing, several mutations were mapped to two genes involved in amino acids transport, suggesting that BMAA was taken up through amino acid transporters. This conclusion was supported by the protective effect of several amino acids against BMAA toxicity. Furthermore, targeted inactivation of genes encoding different amino acid transport pathways conferred various levels of resistance to BMAA. One mutant inactivating all three major amino acid transport systems could no longer take up BMAA and gained full resistance to BMAA toxicity. Therefore, BMAA is a substrate of amino acid transporters, and cyanobacteria are interesting models for genetic analysis of BMAA transport and metabolism.

scholarly journals A new family of proteins (rBAT and 4F2hc) involved in cationic and zwitterionic amino acid transport: a tale of two proteins in search of a transport function.

1994 ◽  
Vol 196 (1) ◽  
pp. 123-137 ◽  
Author(s):  
M Palacín
Keyword(s):  
Amino Acids ◽  
Small Intestine ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Cdna Clones ◽  
Missense Mutations ◽  
Acid Transport ◽  
High Affinity

The currently identified cDNA clones of mammalian amino acid transporters can be grouped into five different families. One family is composed of the proteins rBAT and the heavy chain (hc) of the cell surface antigen 4F2. RNAs encoding these two proteins induce a system b(o,+)-like (rBAT) and a system y+L-like (4F2hc) activity in Xenopus oocytes. Surprisingly, rBAT and 4F2hc do not seem to be pore-forming proteins. This finding supports the hypothesis that rBAT and 4F2hc are subunits or modulators of the corresponding amino acid transport systems. Expression of rBAT in oocytes induces high-affinity transport of cystine, which is shared with transport of cationic and zwitterionic amino acids. The rBAT gene is expressed mainly in kidney and small intestine. The rBAT protein is localized to the microvilli of proximal straight tubules of the kidney and mucosa from the small intestine. This finding is consistent with the involvement of rBAT in a high-affinity resorption system for cystine in the proximal straight tubule of the nephron. All of these characteristics suggest that rBAT is a good candidate for a cystinuria gene. Cystinuria is an inheritable defect in high-affinity transport of cystine, shared with cationic amino acids, through epithelial cells of the renal tubule and intestinal tract. Very recently, point missense mutations have been found in the rBAT gene of cystinuria patients. The most frequent rBAT mutation, M467T (threonine substitution of methionine at residue 467) nearly abolished the amino acid transport activity elicited by rBAT in oocytes. This result offers convincing evidence that rBAT is a cystinuria gene. Biochemical, cytological and genetic approaches are now needed to delineate the mechanism of action of rBAT and 4F2hc in the transport of amino acids.

Amino Acid Transport in a Water-mould: The Possible Regulatory Roles of Calcium and N6-(Δ2-isopentenyl)adenine

1975 ◽  
Vol 53 (9) ◽  
pp. 975-988 ◽  
Author(s):  
Danny P. Singh ◽  
Hérb. B. LéJohn
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Osmotic Shock ◽  
Inhibitory Effect ◽  
Transport Systems ◽  
Acid Transport ◽  
Isopentenyl Adenine ◽  
Energy Dependent ◽  
Water Mould

Transport of amino acids in the water-mould Achlya is an energy-dependent process. Based on competition kinetics and studies involving the influence of pH and temperature on the initial transport rates, it was concluded that the 20 amino acids (L-isomers) commonly found in proteins were transported by more than one, possibly nine, uptake systems. This is similar to the pattern elucidated for some bacteria but unlike those uncovered for all fungi studied to date. The nine different transport systems elucidated are: (i) methionine, (ii) cysteine, (iii) proline, (iv) serine–threonine, (v) aspartic and glutamic acids, (vi) glutamine and asparagine, (vii) glycine and alanine, (viii) histidine, lysine, and arginine, and (ix) phenylalanine–tyrosine–tryptophan and leucine–isoleucine–valine as two overlapping groups. Transport of all of these amino acids was inhibited by azide, cyanide, and its derivatives and 2,4-dinitrophenol. These agents normally interfere with metabolism at the level of the electron transport chain and oxidative phosphorylation. Osmotic shock treatment of the cells released, into the shock fluid, a glycopeptide that binds calcium as well as tryptophan but no other amino acid. The shocked cells are incapable of concentrating amino acids, but remain viable and reacquire this capacity when the glycopeptide is resynthesized.Calcium played more than a secondary role in the transport of the amino acids. When bound to the membrane-localized glycopeptide, it permits concentrative transport to take place. However, excess calcium can inhibit transport which can be overcome by chelating with citrate. Calculations show that the concentration of free citrate is most important. At low citrate concentrations (less than 1 mM) in the absence of exogenously supplied calcium, enhancement of amino acid transport occurs. At high concentrations (greater than 5 mM), citrate inhibits but this effect can be reversed by titrating with calcium. Evidently, the glycopeptide acts as a calcium sink to regulate the concentration of calcium made available to the cell for its membrane activities.N6-(Δ2-isopentenyl) adenine (a plant growth 'hormone') and analogues mimic the inhibitory effect of citrate and bind to the glycopeptide as well. Replot data for citrate and N6-(Δ2-isopentyl) adenine inhibition indicate that both agents have no more than one binding constant. These results implicate calcium, glycopeptide, and energy-dependent transport of solutes in some, as yet undefinable, way.

The contribution of nitrate respiration to the energy budget of the symbiont-containing clam Lucinoma aequizonata: a calorimetric study

1996 ◽  
Vol 199 (2) ◽  
pp. 427-433
Author(s):  
U Hentschel ◽  
S Hand ◽  
H Felbeck
Keyword(s):  
Heat Production ◽  
Sea Water ◽  
Anaerobic Respiration ◽  
Gill Tissue ◽  
Nitrate Respiration ◽  
Heat Output ◽  
Marine Bivalve ◽  
Calorimetric Study ◽  
Perfusion Medium ◽  
Terminal Electron Acceptor

Heat production and nitrate respiration rates were measured simultaneously in the gill tissue of Lucinoma aequizonata. This marine bivalve contains chemoautotrophic, intracellular, bacterial symbionts in its gill tissue. The symbionts show constitutive anaerobic respiration, using nitrate instead of oxygen as a terminal electron acceptor. An immediate increase in heat production was observed after the addition of nitrate to the perfusion medium of the calorimeter and this was accompanied by the appearance of nitrite in the effluent sea water. The nitrate-stimulated heat output was similar under aerobic and anaerobic conditions, which is consistent with the constitutive nature of nitrate respiration. The amount of heat released was dependent on the concentration of nitrate in the perfusion medium. At nitrate concentrations between 0.5 and 5 mmol l-1, the total heat production was increased over twofold relative to unstimulated baseline values. A mean (±s.e.m.) experimental enthalpy of -130±22.6 kJ mol-1 nitrite (N=13) was measured for this concentration range.

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