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PubMed1997

NH3- and CO2-induced suppression of taste nerve responses in clawed toads and eels.

We investigated the effects of intracellular pH values (pHi) on taste nerve responses of clawed toads and eels. (1) CO2, NH3 or trimethylamine reversibly suppressed the taste nerve responses of clawed toads to various amino acids, CaCl2 and caffeine. IC50 values of the suppression of the responses to 0.1 mM L-proline were as follows: approximately 10 mM for CO2, approximately 0.3 mM for NH3, approximately 0.2 mM for trimethylamine. (2) Cross-adaptation experiments showed that L-proline, caffeine and CaCl2 stimulated different receptor sites from each other, indicating the suppressive effect was non-specific. (3) Although CO2, NH3 or trimethylamine yielded the charged molecules, HCO3-, CO3(2-), NH4+ or trimethylammonium on hydration, none of these charged species suppressed taste responses. (4) NH3 increased the threshold concentration of L-proline by e-fold per 0.37 mM NH3 and decreased the maximum response to L-proline with increasing NH3 concentration. (5) The taste nerve responses of eels to 0.1 mM L-arginine, a potent stimulus on eel taste receptors, were similarly suppressed by NH3 with an IC50 value of approximately 0.3 mM. (6) These results indicated that these uncharged species changed pHi, which suppressed the taste responses. CO2-induced acidosis and NH3- or trimethylamine-induced alkalosis are likely to inhibit activities of ion channels or enzymes involved in taste transduction mechanisms.

Ammonia↗
PubMed2005

Community level analysis: genetic and biogeochemical approaches to investigate community composition and function in aerobic ammonia oxidation.

Aerobic ammonia oxidation is the process that converts ammonium to nitrate and thus links the regeneration of organic nitrogen to fixed nitrogen loss by denitrification. It is performed by a phylogenetically restricted group of Proteobacteria (ammonia-oxidizing bacteria, AOB) that are autotrophic and obligately aerobic. This chapter describes methods for the measurement of ammonia oxidation in the environment, with a focus on seawater systems and stable isotopic tracer methods. It also summarizes the current state of molecular ecological approaches for detection of AOB in the environment and characterization of the composition of AOB assemblages.

Ammonia↗
PubMed2006

Molecular dynamics simulations on the Escherichia coli ammonia channel protein AmtB: mechanism of ammonia/ammonium transport.

Molecular dynamics (MD) simulations have been performed at the atomic level to study the ammonium/ammonia transport across the Escherichia coli AmtB membrane protein. Although ammonia primarily exists in the form of NH(4)(+) in aqueous solution, the recent X-ray structure determination of AmtB reveals that the ammonium/ammonia transporter proteins are ammonia-conducting channels rather than ammonium ion transporters [Khademi, S.; et al. Science 2004, 305, 1587; Zheng, L.; et al. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 17090]. Our simulations showed that the entrance of NH(4)(+) into the periplasmic recruitment vestibule requires only 3.1 kcal/mol of energy. This is consistent with the X-ray crystal structure, where one NH(4)(+) is captured in the binding vestibule. In this vestibule, NH(4)(+) loses one water of hydration, but the loss is compensated by a hydrogen bond, first with the backbone carbonyl oxygen of Phe161 then with the hydroxyl group of Ser219, as well as the stabilizing pi-cation interactions with the aromatic rings of Trp148 and Phe107 in the AmtB protein. In the end of this recruitment vestibule, the phenyl ring of Phe107 dynamically switches to an open state. This is correlated with a slight rotation and shifting of the indole ring of Trp148, which eventually creates a slot for the initially buried carboxylate group of Asp160 to become exposed to the bulk solvent. A hydrogen bond wire between NH(4)(+) and the carboxylate group of Asp160 via two water molecules was observed. Thus, Asp160 is most likely the proton acceptor from NH(4)(+). This explains the high conservation of Asp160 in Amt proteins and why the D160A mutant would completely quench the activity of AmtB [Javelle, A.; et al. J. Biol. Chem. 2004, 279, 8530; Marini, A. M.; et al. Curr. Genet. 2006, 49, 364]. Once NH(4)(+) deprotonates, the phenyl ring of Phe215 rotates to open, and the subsequent passage of NH(3) through the channel is straightforward.

Ammonia↗
PubMed2002

Ammonium/methylammonium transport (Amt) proteins facilitate diffusion of NH3 bidirectionally.

The ammonium/methylammonium transport (Amt) proteins of enteric bacteria and their homologues, the methylammonium/ammonium permeases of Saccharomyces cerevisiae, are required for fast growth at very low concentrations of the uncharged species NH(3). For example, they are essential at low ammonium (NH(4)+ + NH(3)) concentrations under acidic conditions. Based on growth studies in batch culture, the Amt protein of Salmonella typhimurium (AmtB) cannot concentrate either NH(3) or NH(4)+ and this organism appears to have no means of doing so. We now show that S. typhimurium releases ammonium into the medium when grown on the alternative nitrogen source arginine and that outward diffusion of ammonium is enhanced by the activity of AmtB. The latter result indicates that AmtB acts bidirectionally. We also confirm a prediction that the AmtB protein would be required at pH 7.0 in ammonium-limited continuous culture, i.e., when the concentration of NH(3) is < or =50 nM. Together with our previous studies, current results are in accord with the view that Amt and methylammonium/ammonium permease proteins increase the rate of diffusion of the uncharged species NH(3) across the cytoplasmic membrane. These proteins are examples of protein facilitators for a gas.

Ammonia↗
PubMed2006

Glutamine synthetase-glutamate synthase pathway and glutamate dehydrogenase play distinct roles in the sink-source nitrogen cycle in tobacco.

Glutamate (Glu) metabolism and amino acid translocation were investigated in the young and old leaves of tobacco (Nicotiana tabacum L. cv Xanthi) using [15N]ammonium and [2-15N]Glu tracers. Regardless of leaf age, [15N]ammonium assimilation occurred via glutamine synthetase (GS; EC 6.1.1.3) and Glu synthase (ferredoxin [Fd]-GOGAT; EC 1.4.7.1; NADH-GOGAT; EC 1.4.1.14), both in the light and darkness, and it did not depend on Glu dehydrogenase (GDH; EC 1.4.1.2). The [15N]ammonium and ammonium accumulation patterns support the role of GDH in the deamination of [2-15N]Glu to provide 2-oxoglutarate and [15N]ammonium. In the dark, excess [15N]ammonium was incorporated into asparagine that served as an additional detoxification molecule. The constant Glu levels in the phloem sap suggested that Glu was continuously synthesized and supplied into the phloem regardless of leaf age. Further study using transgenic tobacco lines, harboring the promoter of the GLU1 gene (encoding Arabidopsis [Arabidopsis thaliana] Fd-GOGAT) fused to a GUS reporter gene, revealed that the expression of Fd-GOGAT remained higher in young leaves compared to old leaves, and higher in the veins compared to the mesophyll. Confocal laser-scanning microscopy localized the Fd-GOGAT protein to the phloem companion cells-sieve element complex in the leaf veins. The results are consistent with a role of Fd-GOGAT in supplying Glu for the synthesis and transport of amino acids. Taken together, the data provide evidence that the GS-GOGAT pathway and GDH play distinct roles in the source-sink nitrogen cycle of tobacco leaves.

Amides↗
PubMed1994

Regulation of intracellular pH in crypt cells from rabbit distal colon.

H+ secretory mechanisms and intrinsic intracellular buffering capacity were studied in crypt cells from rabbit distal colon. To this end crypts of Lieberkühn were isolated by microdissection, and intracellular pH (pHi) was measured using digital imaging fluorescence microscopy and the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)- 5(6)-carboxyfluorescein. In the absence of HCO(3-)-CO2 and presence of Na+, resting pHi was 7.51 +/- 0.04 (n = 237/23, cells/crypts). However, 6 min after superfusion with a solution containing zero Na+, 1 x 10(5) M Sch-28080 and 5 x 10(-8) M bafilomycin A1, pHi in cells at the bottom of the crypts was significantly reduced, whereas pHi in cells at the top of the crypts remained unchanged. The intrinsic buffering capacity of cells from the middle to the top portion of crypts was significantly higher in the pHi range 7.2-7.6 than of cells at the bottom of the crypt. H+ secretion after an NH(4+)-NH3 pulse amounted to 245 +/- 53 microM/s (n = 73/7) at pHi 7.1 and was largely Na+ dependent and ethylisopropylamiloride sensitive. The Na(+)-independent recovery of pHi after an acid load was insensitive to Sch-28080 and bafilomycin A1. In conclusion, pHi in colonic crypt cells is regulated through Na+/H+ exchange activity in the absence of HCO3-. In addition, intracellular buffering capacity varied with the position along the crypt axis, whereas Na+/H+ exchange activity and pHi did not.

Amiloride↗
PubMed2001

Effect of acute exposure to ammonia on glutamate transport in glial cells isolated from the salamander retina.

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 of L-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.

ATP-Binding Cassette Transporters↗
PubMed1976

Corn grain preserved with ammonium isobutyrate for lactating dairy cattle.

Twenty-four lactating cows were fed one of three complete rations containing dry corn, ensiled corn, or corn treated with ammonium isobutyrate in a Latin square arrangement of treatments. Two weeks were used for adjustments to rations and 3 wk for collection of data. There were no differences in average daily yield of milk or fat-corrected milk, but fat percentage of milk from cows fed ensiled corn was lower than that of those given dry corn. Fat test of cows fed treated corn was intermediate and not different from the other groups. Molar proportions of volatile fatty acids and concentrations of rumen ammonia were not different among treatments.

Ammonia↗
PubMed2001

A method for the determination of volatile ammonia in air, using a nitrogen-cooled trap and fluorometric detection.

A quick, cheap, and accurate method for the determination of ammonia in air is described. Ammonia and water vapor are trapped simultaneously in a gas sampling tube cooled in liquid nitrogen. Subsequently ammonia is derivatized with o-phthaldialdehyde and determined using fluorescence detection. The detection limit of ammonia in a gaseous sample is about 1 nmol per liter of gas. The recovery, using a calibration gas of 6.00 ppm ammonia in nitrogen, is 102.9 +/- 6.4%. Examples are presented in which this method is used for the determination of ammonia in environmental air and in expired air during exhaustive exercise of a human subject. It is suggested that this method can be used for the determination of volatile ammonia and other compounds in air during environmental and biological monitoring and in research.

Air↗
PubMed1991

Alkalinity of non-industrial cleaning products and the likelihood of producing significant esophageal burns.

Alkaline cleaning products are a cause of serious esophageal injury. Over time, legislation has diminished the concentration of many such non-industrial solutions and solids; however several products presently do not list either the pH or relative concentrations of alkaline constituents. This study measures the pHs of several non-industrial cleaning products containing either ammonium chloride, sodium hydroxide, or potassium hydroxide. Three pH measurements were performed on each of 10 non-industrial alkaline cleaning products (eight liquid, two solid). Two 0.1% ammonium chloride solutions had pHs of 12.06 +/- 0.00 and 12.06 +/- 0.01, whereas a pH of 12.43 +/- 0.00 was recorded in a 0.2% ammonium chloride solution. Concentrations of sodium hydroxide and potassium hydroxide were listed on only one of five liquid cleaning product labels. The pHs for these five products varied between 12.83 +/- 0.009 and 13.5 +/- .0.2. The pHs of three sodium hydroxide solutions differed from values reported in Micromedex (Micromedex Inc, Denver CO) by up to 0.32 pH units. Ten percent (v/v) solutions of two solid lye products had pHs of 13.62 +/- 0.008 and 13.74 +/- 0.02. The investigator found that selected non-industrial cleaning products, including ammonia solutions, retain the ability to cause clinically important esophageal damage.

Ammonium Chloride↗
PubMed2003

Glucose alleviates ammonia-induced inhibition of short-chain fatty acid metabolism in rat colonic epithelial cells.

Ammonia decreased metabolism by rat colonic epithelial cells of butyrate and acetate to CO2 and ketones but increased oxidation of glucose and glutamine. Ammonia decreased cellular concentrations of oxaloacetate for all substrates evaluated. The extent to which butyrate carbon was oxidized to CO2 after entering the tricarboxylic acid (TCA) cycle was not significantly influenced by ammonia, suggesting there was no major shift toward efflux of carbon from the TCA cycle. Ammonia reduced entry of butyrate carbon into the TCA cycle, and the proportion of CoA esterified with acetate and butyrate correlated positively with the production of CO2 and ketone bodies. Also, ammonia reduced oxidation of propionate but had no effect on oxidation of 3-hydroxybutyrate. Inclusion of glucose, lactate, or glutamine with butyrate and acetate counteracted the ability of ammonia to decrease their oxidation. In rat colonocytes, it appears that ammonia suppresses short-chain fatty acid (SCFA) oxidation by inhibiting a step before or during their activation. This inhibition is alleviated by glucose and other energy-generating compounds. These results suggest that ammonia may only affect SCFA metabolism in vivo when glucose availability is compromised.

3-Hydroxybutyric Acid↗
PubMed1997

Effect of intracellular pH on agonist-induced [Ca2+]i transients in HT29 cells.

In this study we examined the influence of intracellular pH (pHi) on agonist-induced changes of intracellular Ca2+ activity ([Ca2+]i) in HT29 cells. pHi and [Ca2+]i were measured microspectrofluorimetrically using BCECF and fura-2, respectively. Buffers containing trimethylamine (TriMA), NH3/NH4+ and acetate were used to clamp pHi to defined values. The magnitudes of the peak and plateau of [Ca2+]i transients induced by carbachol (CCH, 10(-6) mol/l) were greatly enhanced by an acidic pHi and nearly abolished by an alkaline pHi. The relationship between pHi and the [Ca2+]i peak was nearly linear from pHi 7.0 to 7.8. This effect of pHi was also observed at higher CCH concentrations (10(-4 )and 10(-5) mol/l), at which the inhibitory effect of an alkaline pHi was more pronounced than the stimulatory effect of an acidic pHi. An acidic pHi shifted the CCH concentration/response curve to the left, whereas an alkaline pHi led to a rightward shift. The influence of pHi on [Ca2+]i transients induced by neurotensin (10(-8) mol/l) or ATP (5 x 10(-7) mol/l) was similar to its influence on those induced by CCH, but generally not as pronounced. Measurements of cellular inositol 1,4,5-trisphosphate (InsP3) showed no changes in response to acidification with acetate (20 mmol/l) or alkalinization with TriMA (20 mmol/l). The InsP3 increase induced by CCH was unaltered at an acidic pHi, but was augmented at an alkaline pHi. Confocal measurements of cell volume showed no significant changes induced by TriMA or acetate. Slow-whole-cell patch-clamp experiments showed no additional effect of CCH on the membrane voltage (Vm) measured after TriMA or acetate application. We conclude that pHi is a physiological modulator of hormonal effects in HT29 cells, as the [Ca2+]i responses to agonists were significantly changed at already slightly altered pHi. The measurements of InsP3, cell volume and Vm show that pHi must act distally to the InsP3 production, and not via changes of cell volume or Vm.

Acetates↗