scholarly journals Taurine transporter (TauT) deficiency impairs ammonia detoxification in mouse liver

2019 ◽  
Vol 116 (13) ◽  
pp. 6313-6318 ◽  
Author(s):  
Natalia Qvartskhava ◽  
Cheng Jun Jin ◽  
Tobias Buschmann ◽  
Ute Albrecht ◽  
Johannes Georg Bode ◽  
...  
Keyword(s):  
Liver Perfusion ◽  
Ammonia Concentration ◽  
Tyrosine Nitration ◽  
Taurine Transporter ◽  
Tissue Integrity ◽  
Plot Analysis ◽  
Rna Oxidation ◽  
Dependent Inactivation ◽  
Ammonia Transport ◽  
Glutamine Synthesis

Hepatic ammonia handling was analyzed in taurine transporter (TauT) KO mice. Surprisingly, hyperammonemia was present at an age of 3 and 12 months despite normal tissue integrity. This was accompanied by cerebral RNA oxidation. As shown in liver perfusion experiments, glutamine production from ammonia was diminished in TauT KO mice, whereas urea production was not affected. In livers from 3-month-old TauT KO mice protein expression and activity of glutamine synthetase (GS) were unaffected, whereas the ammonia-transporting RhBG protein was down-regulated by about 50%. Double reciprocal plot analysis of glutamine synthesis versus perivenous ammonia concentration revealed that TauT KO had no effect on the capacity of glutamine formation in 3-month-old mice, but doubled the ammonia concentration required for half-maximal glutamine synthesis. Since hepatic RhBG expression is restricted to GS-expressing hepatocytes, the findings suggest that an impaired ammonia transport into these cells impairs glutamine synthesis. In livers from 12-, but not 3-month-old TauT KO mice, RhBG expression was not affected, surrogate markers for oxidative stress were strongly up-regulated, and GS activity was decreased by 40% due to an inactivating tyrosine nitration. This was also reflected by kinetic analyses in perfused liver, which showed a decreased glutamine synthesizing capacity by 43% and a largely unaffected ammonia concentration dependence. It is concluded that TauT deficiency triggers hyperammonemia through impaired hepatic glutamine synthesis due to an impaired ammonia transport via RhBG at 3 months and a tyrosine nitration-dependent inactivation of GS in 12-month-old TauT KO mice.

Effect of Acute Exposure to Ammonia on Glutamate Transport in Glial Cells Isolated From the Salamander Retina

2001 ◽  
Vol 86 (2) ◽  
pp. 836-844 ◽  
Author(s):  
Dominic Mort ◽  
Païkan Marcaggi ◽  
James Grant ◽  
David Attwell
Keyword(s):  
Glial Cells ◽  
Glutamate Uptake ◽  
Ph Dependence ◽  
Glutamate Transporter ◽  
Ammonia Concentration ◽  
Ammonia Level ◽  
Glutamate Transport ◽  
Acute Exposure ◽  
Ph Change ◽  
Glutamine Synthesis

A rise of brain ammonia level, as occurs in liver failure, initially increases glutamate accumulation in neurons and glial cells. We investigated the effect of acute exposure to ammonia on glutamate transporter currents in whole cell clamped glial cells from the salamander retina. Ammonia potentiated the current evoked by a saturating concentration ofl-glutamate, and decreased the apparent affinity of the transporter for glutamate. The potentiation had a Michaelis-Menten dependence on ammonia concentration, with a K m of 1.4 mM and a maximum potentiation of 31%. Ammonia also potentiated the transporter current produced by d-aspartate. Potentiation of the glutamate transport current was seen even with glutamine synthetase inhibited, so ammonia does not act by speeding glutamine synthesis, contrary to a suggestion in the literature. The potentiation was unchanged in the absence of Cl− ions, showing that it is not an effect on the anion current gated by the glutamate transporter. Ammonium ions were unable to substitute for Na+in driving glutamate transport. Although they can partially substitute for K+ at the cation counter-transport site of the transporter, their occupancy of these sites would produce a potentiation of <1%. Ammonium, and the weak bases methylamine and trimethylamine, increased the intracellular pH by similar amounts, and intracellular alkalinization is known to increase glutamate uptake. Methylamine and trimethylamine potentiated the uptake current by the amount expected from the known pH dependence of uptake, but ammonia gave a potentiation that was larger than could be explained by the pH change, and some potentiation of uptake by ammonia was still seen when the internal pH was 8.8, at which pH further alkalinization does not increase uptake. These data suggest that ammonia speeds glutamate uptake both by increasing cytoplasmic pH and by a separate effect on the glutamate transporter. Approximately two-thirds of the speeding is due to the pH change.

scholarly journals A New Analysis of Ammonia and Sodium Transport Through the Gills of the Freshwater Rainbow Trout (Salmo Gairdneri)

1989 ◽  
Vol 142 (1) ◽  
pp. 155-175 ◽  
Author(s):  
MARTINE AVELLA ◽  
MICHEL BORNANCIN
Keyword(s):  
Sodium Transport ◽  
Proton Transport ◽  
External Medium ◽  
Ammonia Excretion ◽  
Gill Tissue ◽  
Ammonia Concentration ◽  
Salmo Gairdneri ◽  
Sodium Absorption ◽  
Ammonia Transport ◽  
The Relationship

The mechanism of ammonia excretion and sodium absorption was re-examined in trout using the isolated-perfused head preparation. Preliminary experiments in which ammonia concentration was increased on the blood side (internal) showed that ammonia and sodium transport was uncoupled. For ammonia excretion, our results showed that gill tissue endogenously produces ammonia. A correlation was demonstrated between ammonia excretion and the internal-external ammonia gradient. We conclude that diffusion in the form of NH3 was responsible for ammonia efflux and we were therefore able to estimate its diffusion coefficient (DNH3 = 1.55×10−6cm2s−1) and permeability coefficient (6×10−3cm s−1). This ammonia diffusion was shown to be modified according to the external proton availability. For sodium absorption, significant changes were caused by indirect modifications of intracellular pH brought about by addition of acetazolamide inside or ammonia outside or by acidification of the internal or external medium. The relationship between sodium and proton transport was further confirmed by the action of the drug amiloride and the measurement of H+ excretion. A possible model representing sodium, proton and ammonia transport through the gill epithelium is proposed.

scholarly journals Methionine Sulfoximine, a Glutamine Synthetase Inhibitor, Attenuates Increased Extracellular Potassium Activity during Acute Hyperammonemia

1997 ◽  
Vol 17 (1) ◽  
pp. 44-49 ◽  
Author(s):  
Hideyoshi Sugimoto ◽  
Raymond C. Koehler ◽  
David A. Wilson ◽  
Saul W. Brusilow ◽  
Richard J. Traystman
Keyword(s):  
Glutamine Synthetase ◽  
Sodium Acetate ◽  
Ammonium Acetate ◽  
Ammonia Concentration ◽  
Methionine Sulfoximine ◽  
Extracellular Potassium ◽  
Edema Formation ◽  
Plasma Ammonia ◽  
Glutamine Synthesis ◽  
Ion Sensitive Microelectrodes

Hyperammonemia causes glutamine accumulation and astrocyte swelling. Inhibition of glutamine synthesis reduces ammonia-induced edema formation and watery swelling in astrocyte processes. Ordinarily, astrocytes tightly control extracellular K+ activity [K+]e. We tested the hypothesis that acute hyperammonemia interferes with this tight regulation such that [K+]e increases and that inhibition of glutamine synthetase reduces this increase in [K+]e. Ion-sensitive microelectrodes were used to measure [K+]e in parietal cortex continuously over a 6-h period in anesthetized rats. After i.v. sodium acetate infusion in eight control rats, plasma ammonia concentration was 33 ± 26 μmol/L (± SD) and [K+]e remained stable at 4.3 ± 1.6 mmol/L. During ammonium acetate infusion in nine rats, plasma ammonia increased to 594 ± 124 μmol/L at 2 h and to 628 ± 135 μmol/L at 6 h. There was a gradual increase in [K+]e from 3.9 ± 0.7 to 6.8 ± 2.7 mmol/L at 2 h and 11.8 ± 6.7 mmol/L at 6 h. In eight rats, L-methionine-D,L-sulfoximine (150 mg/kg) was infused 3 h before ammonium acetate infusion to inhibit glutamine synthetase. At 2 and 6 h of ammonium acetate infusion, plasma ammonia concentration was 727 ± 228 and 845 ± 326 μmol/L, and [K+]e was 4.5 ± 1.9 and 6.1 ± 3.8 mmol/L, respectively. The [K+]e value at 6 h was significantly less than that obtained with ammonium acetate infusion alone but was not different from that obtained with sodium acetate infusion. We conclude that acute hyperammonemia impairs astrocytic control of [K+]e and that this impairment is linked to glutamine accumulation rather than ammonium ions per se.

scholarly journals Dependence of in vivo glutamine synthetase activity on ammonia concentration in rat brain studied by 1H - 15N heteronuclear multiple-quantum coherence-transfer NMR

1995 ◽  
Vol 311 (2) ◽  
pp. 681-688 ◽  
Author(s):  
K Kanamori ◽  
B D Ross ◽  
E L Kuo
Keyword(s):  
Quantum Coherence ◽  
Ammonia Concentration ◽  
Multiple Quantum ◽  
Blood Ammonia ◽  
Coherence Transfer ◽  
Heteronuclear Multiple Quantum Coherence ◽  
Glutamine Synthesis ◽  
Gaba Synthesis ◽  
Multiple Quantum Coherence

The dependence of the in vivo rate of glutamine synthesis on the substrate ammonia concentration was studied in rat brain by 1H-15N heteronuclear multiple-quantum coherence-transfer NMR in combination with biochemical techniques. In vivo rates were measured at various steady-state blood and brain ammonia concentrations within the ranges 0.4-0.55 mumol/g and 0.86-0.98 mumol/g respectively, after low-rate intravenous 15NH4+ infusion (isotope chase). The rate of glutamine synthesis at steady state was determined from the change in brain [5-15N]glutamine levels during isotope chase, observed selectively through the amide proton by NMR, and 15N enrichments of brain glutamine and of blood and brain ammonia measured byN gas chromatography-MS. The in vivo rate (v) was 3.3-4.5 mumol/h per g of brain at blood ammonia concentrations (s) of 0.40-0.55 mumol/g. A linear increase of 1/v with 1/s permitted estimation of the in vivo glutamine synthetase (GS) activity at a physiological blood ammonia concentration to be 0.4-2.1 mumol/h per g. The observed ammonia-dependence strongly suggests that, under physiological conditions, in vivo GS activity is kinetically limited by sub-optimal in situ concentrations of ammonia as well as glutamate and ATP. Comparison of the observed in vivo GS activity with the reported in vivo rates of glutaminase and of gamma-aminobutyrate (GABA) synthesis suggests that, under mildly hyperammonaemic conditions, glutamine is synthesized at a sufficiently high rate to serve as a precursor of GABA, but glutaminase-catalysed hydrolysis of glutamine is too slow to be the sole provider of glutamate used for GABA synthesis.

scholarly journals Involvement of TauT/SLC6A6 in Taurine Transport at the Blood–Testis Barrier

Metabolites ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 66
Author(s):  
Yoshiyuki Kubo ◽  
Sakiko Ishizuka ◽  
Takeru Ito ◽  
Daisuke Yoneyama ◽  
Shin-ichi Akanuma ◽  
...  
Keyword(s):  
Aminobutyric Acid ◽  
Seminiferous Tubules ◽  
Taurine Transporter ◽  
Taurine Transport ◽  
Plot Analysis ◽  
Influx Transport ◽  
Dependent Inhibition ◽  
Taurine Uptake ◽  
Sertoli Cell Line ◽  
Blood Testis Barrier

Taurine transport was investigated at the blood–testis barrier (BTB) formed by Sertoli cells. An integration plot analysis of mice showed the apparent influx permeability clearance of [3H]taurine (27.7 μL/(min·g testis)), which was much higher than that of a non-permeable paracellular marker, suggesting blood-to-testis transport of taurine, which may involve a facilitative taurine transport system at the BTB. A mouse Sertoli cell line, TM4 cells, showed temperature- and concentration-dependent [3H]taurine uptake with a Km of 13.5 μM, suggesting that the influx transport of taurine at the BTB involves a carrier-mediated process. [3H]Taurine uptake by TM4 cells was significantly reduced by the substrates of taurine transporter (TauT/SLC6A6), such as β-alanine, hypotaurine, γ-aminobutyric acid (GABA), and guanidinoacetic acid (GAA), with no significant effect shown by L-alanine, probenecid, and L-leucine. In addition, the concentration-dependent inhibition of [3H]taurine uptake revealed an IC50 of 378 μM for GABA. Protein expression of TauT in the testis, seminiferous tubules, and TM4 cells was confirmed by Western blot analysis and immunohistochemistry by means of anti-TauT antibodies, and knockdown of TauT showed significantly decreased [3H]taurine uptake by TM4 cells. These results suggest the involvement of TauT in the transport of taurine at the BTB.

Ammonia transport in a mathematical model of rat proximal tubule

1994 ◽  
Vol 267 (2) ◽  
pp. F237-F248 ◽  
Author(s):  
A. M. Weinstein
Keyword(s):  
Proximal Tubule ◽  
Cell Membranes ◽  
Ammonia Concentration ◽  
K Channel ◽  
Na Pump ◽  
Relative Contribution ◽  
Luminal Membrane ◽  
Ammonia Transport ◽  
Total Ammonia ◽  
Rat Proximal Tubule

Pathways for ammonia transport have been incorporated within a model of rat proximal tubule [A. M. Weinstein. Am. J. Physiol. 263 (Renal Fluid Electrolyte Physiol. 32): F784-F798, 1992]. The luminal membrane includes a Na+/NH4+ exchanger, while at the peritubular membrane there is uptake of NH4+ on the Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase); both luminal and peritubular cell membranes contain conductive pathways for NH4+. The model equations have been expanded to include cellular ammoniagenesis. The principal focus of this study is the interplay of forces that can raise proximal tubule fluid total ammonia concentration 10-fold higher than in arterial plasma. Analysis of a cellular model reveals that luminal membrane Na+/NH4+ exchange, cellular production of ammonia, and peritubular membrane NH4+ uptake (via Na(+)-K(+)-ATPase or via K+ channel) all act in parallel to drive ammonia secretion. This derives from the cellular interconversion of NH4+ and NH3 and the free permeation of NH3 across cell membranes. It implies that inhibition of the luminal membrane transporter does not block the contribution of peritubular uptake to the overall active transport of ammonia. Conversely, when inhibition of the luminal membrane Na+/NH4+ entry (i.e., Na+/H+ inhibition) depresses transcellular Na+ flux, then the decrease of NH4+ flux through the peritubular Na+ pump enhances the apparent importance of the luminal membrane pathway. This analysis is confirmed in the numerical calculations and is a departure from the Ussing paradigm of series membrane Na+ transport. Although active secretion of ammonia by this tubule is substantial, the relative contribution of luminal Na+/NH4+ exchange and of peritubular uptake via the Na+ pump remains uncertain. The determination of peritubular capillary NH4+ concentration will be crucial to resolving this uncertainty, with lower concentration (i.e., closer to systemic arterial ammonia) obligating greater luminal membrane Na+/NH4+ exchange.

Ketone body effects on glutamine metabolism in isolated kidneys and mitochondria

1982 ◽  
Vol 243 (2) ◽  
pp. F181-F187
Author(s):  
L. Goldstein ◽  
R. J. Solomon ◽  
D. F. Perlman ◽  
P. M. McLaughlin ◽  
M. A. Taylor
Keyword(s):  
Ammonia Concentration ◽  
Glutamine Metabolism ◽  
Ammonia Production ◽  
Glutamine Concentration ◽  
Marked Inhibition ◽  
End Products ◽  
Nadh Ratio ◽  
Glutamine Synthesis ◽  
Beta Hydroxybutyrate ◽  
Isolated Kidneys

beta-Hydroxybutyrate (but not acetoacetate) caused marked inhibition of ammonia production and glutamine extraction in isolated perfused kidneys from normal rats. Glutamine synthesis was not affected by beta-hydroxybutyrate (BHB). Measurement of metabolite levels in freeze-clamped kidneys showed that BHB increased glutamine concentration, decreased ammonia concentration, and reduced the mitochondrial NAD+/NADH ratio (calculated) in perfused kidneys. BHB inhibited flux through the glutamate dehydrogenase pathway, probably as a result of reduction in the NAD+/NADH ratio, in isolated renal mitochondria. In isolated perfused kidneys from acidotic rats, ammonia production and mitochondrial NAD+/NADH were both elevated and BHB did not inhibit renal ammoniagenesis. Although ammonia production in the acidotic kidneys was not directly related to the mitochondrial NAD+/NADH ratio, the elevation of this ratio may have permitted a normal rate of oxidation of glutamine end products--which is essential for maintaining the elevated ammoniagenesis--to take place in the presence of BHB.

scholarly journals Metabolism of glutamine and glutamic acid by isolated perfused kidneys of normal and acidotic rats

1972 ◽  
Vol 130 (3) ◽  
pp. 671-680 ◽  
Author(s):  
D. A. Hems
Keyword(s):  
Time Course ◽  
Ammonia Concentration ◽  
Tissue Concentrations ◽  
Renal Metabolism ◽  
Rapid Induction ◽  
Ammonia Release ◽  
Glutamine Synthesis ◽  
The Right ◽  
Glucose Formation ◽  
Isolated Kidneys

1. When isolated kidneys from fed rats were perfused with glutamine the rate of ammonia release at pH7.4 (110–360μmol/h per g dry wt.) was one to two times that of glutamine removal. Glucose formation from 5mm-glutamine was 16μmol/h per g. If kidneys were perfused with glutamine at pH7.1 (10–13mm-sodium bicarbonate) there was no increase in glutamine removal or in the formation of ammonia or glucose. 2. When isolated kidneys from fed rats were perfused with glutamate at pH7.4, glucose formation was 59μmol/h per g, glutamine formation was 182μmol/h per g and ammonia release was negligible. At pH7.1 glutamine synthesis was inhibited and formation of ammonia and glucose were increased. 3. In perfused kidneys from acidotic rats, which had received 1.5% (w/v) NH4Cl to drink for 7–10 days, gluconeogenesis from glutamine was enhanced (101μmol/h per g). Glutamine removal and ammonia formation were also increased, compared with the rates in perfused kidney from normal rats. The extra glutamine consumed was equivalent to the extra glucose formed. 4. When the kidney from the 7–10-day-acidotic rat was perfused with glutamate gluconeogenesis was increased (113μmol/h per g). Synthesis of glutamine was decreased, and ammonia release was approximately equal to the rate of glutamate removal. 5. The time-course of these metabolic alterations was investigated after the rapid induction of acidosis by infusion of 0.25m-HCl into the right side of the heart. The increase in gluconeogenesis from glutamine developed gradually over several hours. When kidneys from 6h-acidotic rats were perfused with glutamate, formation of glucose and glutamine were both rapid. 6. In acidotic rat kidneys perfused with glutamine, tissue concentrations of glutamate and glucose 6-phosphate were increased compared with those in control perfused kidneys from non-acidotic rats. 7. The results are discussed in terms of control of the renal metabolism of glutamine. In particular, it is suggested that in acidotic rats glucose formation is the major fate of the carbon of the extra glutamine utilized by the kidney, and that inhibition of glutamine synthetase could contribute to the increase in intracellular ammonia concentration in the kidney.

15N-NMR Spectroscopy Studies of Ammonia Transport and Glutamine Synthesis in the Hyperammonemic Rat Brain

1998 ◽  
Vol 20 (4-5) ◽  
pp. 434-443 ◽  
Author(s):  
Jun Shen ◽  
Nicola R. Sibson ◽  
Gary Cline ◽  
Kevin L. Behar ◽  
Douglas L. Rothman ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Rat Brain ◽  
Ammonia Transport ◽  
Glutamine Synthesis ◽  
Spectroscopy Studies

Ammonia and bicarbonate transport by rat cortical collecting ducts perfused in vitro

1985 ◽  
Vol 249 (6) ◽  
pp. F870-F877 ◽  
Author(s):  
M. A. Knepper ◽  
D. W. Good ◽  
M. B. Burg
Keyword(s):  
Ammonia Concentration ◽  
Bicarbonate Transport ◽  
Bicarbonate Secretion ◽  
Acidic Ph ◽  
Acid Base ◽  
Collecting Ducts ◽  
Trapping Model ◽  
Ammonia Transport ◽  
Total Ammonia

We measured bicarbonate and ammonia transport by isolated perfused cortical collecting ducts from deoxycorticosterone-treated rats. With no ammonia in the perfusate and bath solutions, the collecting ducts secreted bicarbonate. The bicarbonate secretion was prevented when the rats were given 40 mM NH4Cl to drink. When 4 mM total ammonia was added to the perfusate and bath, the collecting ducts secreted ammonia and the direction of bicarbonate transport reversed toward absorption. Under those conditions the collected total ammonia concentration exceeded the value predicted by the diffusion-trapping model, assuming pH equilibrium. However, when carbonic anhydrase was added to the perfusate (to assure pH equilibrium), the collected total ammonia concentration decreased to the level predicted by the diffusion-trapping model. We conclude that rat cortical collecting ducts can secrete bicarbonate at substantial rates; the rate of bicarbonate secretion is modified by changes in the acid-base intake of the rats; ammonia secretion occurs by simple nonionic diffusion in this segment; the ammonia secretion is enhanced by the presence of acidic pH disequilibrium in the lumen; and ammonia in the perfusion and bath solutions inhibits bicarbonate secretion by rat cortical collecting ducts, a response that may be important for the regulation of renal bicarbonate excretion.

Sign in / Sign up

Export Citation Format

Share Document