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At least 631 records · Page 35Linked to original sources
PubMed1998

Chloride concentration in cultured hippocampal neurons increases during long-term exposure to ammonia through enhanced expression of an anion exchanger.

The effects of long-term exposure to ammonia on [Cl-]i in cultured hippocampal neurons were examined. Ammonia increased the [Cl-]i time- (>/=24 h) and concentration- (>/=2 mM) dependently, resulting in a depolarizing shift of the equilibrium potential of the GABAA receptor-Cl- channel opening (EGABA). Such an effect of ammonia was diminished by the inhibitors of Cl-/HCO3- exchangers, 0.1 mM 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) and 0.1 mM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), and a carbonic anhydrase inhibitor, 2 mM acetazolamide, but not by a Na+/K+/2Cl-cotransport inhibitor, 50 microM bumetanide, suggesting an enhanced Cl-/HCO3- exchange activity by ammonia. The ammonia-induced increase in [Cl-]i was also abolished by the inhibitors of protein kinase C (PKC), 0.1 microM calphostin C and 10 microM 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine dihydrochloride (H-7), and of transcription and de novo protein synthesis, 1 microM actinomycin D and 0.5 microg/ml cycloheximide, while a PKC activator, 0.1 h microM phorbor 12-myristate 13-acetate (PMA), increased the [Cl-]i. The mRNA level of the AE3 Cl-/HCO3- exchanger was increased by ammonia in a calphostin C- and H-7-sensitive manner. The AE3-like immunoreactivity was also increased by ammonia. These findings suggest that long-term exposure to ammonia increases the expression of AE3 through the activation of PKC, resulting in an increase in [Cl-]i in neurons and a reduction of inhibitory postsynaptic potentials.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2000

Impact of K(+) homeostasis on net acid secretion in rat terminal inner medullary collecting duct: role of the Na,K-ATPase.

For the past 50 years, the mechanism of ammonium (NH(4)(+)) transport along the collecting duct has been thought to occur through active H(+) section in parallel with the nonionic diffusion of ammonia (NH(3)). This model is supported by two basic experimental observations. First, NH(4)(+) secretion generally correlates with the NH(3) concentration gradient between the interstitium and the collecting duct lumen. This NH(3) gradient is generated through both luminal acidification, which reduces luminal NH(3) concentration, and through countercurrent multiplication, which increases interstitial NH(3) concentration. The result is secretion of NH(3) into the collecting duct lumen down its concentration gradient. Second, because NH(4)(+) permeability is low relative to that of NH(3), there is significant secretion of NH(3) into the collecting duct lumen with minimal back-diffusion of NH(4)(+). However, our laboratory, as well as others, has shown that this model is an oversimplification of the mechanism of NH(4)(+) transport along the collecting duct. NH(4)(+) is transported through a variety of K(+) transport pathways including Na,K-ATPase. K(+) and NH(4)(+) compete for a common extracellular binding site on Na, K-ATPase. During hypokalemia, interstitial K(+) concentration is reduced, which augments NH(4)(+) uptake by the Na(+) pump. In K(+) restriction, Na,K-ATPase-mediated NH(4)(+) uptake provides an important source of H(+) for net acid secretion and for the titration of luminal buffers in the terminal inner medullary collecting duct. This pathway contributes to the increase in NH(4)(+) excretion and metabolic alkalosis observed during hypokalemia.

Ammonia↗
PubMed2001

Diurnal changes in nitrogen assimilation of tobacco roots.

To gain an insight into the diurnal changes of nitrogen assimilation in roots the in vitro activities of cytosolic and plasma membrane-bound nitrate reductase (EC 1.6.6.1), nitrite reductase (EC 1.7.7.1) and cytosolic and plastidic glutamine synthetase (EC 6.3.1.2) were studied. Simultaneously, changes in the contents of total protein, nitrate, nitrite, and ammonium were followed. Roots of intact tobacco plants (Nicotiana tabacum cv. Samsun) were extracted every 3 h during a diurnal cycle. Nitrate reductase, nitrite reductase and glutamine synthetase were active throughout the day-night cycle. Two temporarily distinct peaks of nitrate reductase were detected: during the day a peak of soluble nitrate reductase in the cytosol, in the dark phase a peak of plasma membrane-bound nitrate reductase in the apoplast. The total activities of nitrate reduction were similar by day and night. High activities of nitrite reductase prevented the accumulation of toxic amounts of nitrite throughout the entire diurnal cycle. The resulting ammonium was assimilated by cytosolic glutamine synthetase whose two activity peaks, one in the light period and one in the dark, closely followed those of nitrate reductase. The contribution of plastidic glutamine synthetase was negligible. These results strongly indicate that nitrate assimilation in roots takes place at similar rates day and night and is thus differently regulated from that in leaves.

Cell Membrane↗
PubMed2000

Evaluation of application methods for control of Aspergillus fumigatus proliferation on the air cell membrane of in ovo injected broiler eggs.

Three different techniques of applying fungicides and mold inhibitors were evaluated as control methods for Aspergillus fumigatus proliferation on the air cell membrane of eggs that were infertile or contained early dead embryos following in ovo egg injection. A controlled Aspergillus challenge model was utilized that simulates the natural occurrence of fungal growth following in ovo egg injection. Methods of application examined were egg shell spray, direct air cell application prior to Aspergillus challenge, and micro-aerosol fogging in the incubation compartment during Aspergillus challenge. Fungicides and mold inhibitors used included propionic acid, propionic acid plus ammonia, phenol, quaternary ammonium plus organic tin, hydrogen peroxide, enilconazole, and an aromatase inhibitor. When applied as egg shell spray treatments or micro-aerosol fog treatments, none of the products that were tested significantly reduced the incidence of mold proliferation on the air cell membrane when compared with untreated, but otherwise challenged, controls. When applied directly to the air cell membrane prior to fungal challenge, only enilconazole and the aromatase inhibitor significantly reduced the incidence of fungal proliferation when compared with appropriate controls.

Aerosols↗
PubMed1988

Amino Acid Metabolism of Lemna minor L. : III. Responses to Aminooxyacetate.

Aminooxyacetate, a known inhibitor of transaminase reactions and glycine decarboxylase, promotes rapid depletion of the free pools of serine and aspartate in nitrate grown Lemna minor L. This compound markedly inhibits the methionine sulfoximine-induced accumulation of free ammonium ions and greatly restricts the methionine sulfoximine-induced depletion of amino acids such as glutamate, alanine, and asparagine. These results suggest that glutamate, alanine, and asparagine are normally catabolized to ammonia by transaminase-dependent pathways rather than via dehydrogenase or amidohydrolase reactions. Aminooxyacetate does not inhibit the methionine sulfoximine-induced irreversible deactivation of glutamine synthetase in vivo, indicating that these effects cannot be simply ascribed to inhibition of methionine sulfoximine uptake by amino-oxyacetate. This transaminase inhibitor promotes extensive accumulation of several amino acids including valine, leucine, isoleucine, alanine, glycine, threonine, proline, phenylalanine, lysine, and tyrosine. Since the aminooxyacetate induced accumulations of valine, leucine, and isoleucine are not inhibited by the branched-chain amino acid biosynthesis inhibitor, chlorsulfuron, these amino acid accumulations most probably involve protein turnover. Depletions of soluble protein bound amino acids are shown to be approximately stoichiometric with the free amino acid pool accumulations induced by aminooxyacetate. Aminooxyacetate is demonstrated to inhibit the chlorsulfuron-induced accumulation of alpha-amino-n-butyrate in L. minor, supporting the notion that this amino acid is derived from transamination of 2-oxobutyrate.

Journal Article↗
PubMed1993

Inhibition of slow-wave repolarization and Ca(2+)-activated K+ channels by quaternary ammonium ions.

We studied the effects of the K+ channel blocker tetrapentylammonium (TPeA) on the electrical activity of intact circular smooth muscle from canine colon. TPeA (10 and 20 microM) increased slow-wave duration and "locked" the membrane potential around -30 mV plateau potential after several minutes of application, suggesting that K+ channels are essential for termination of colonic slow waves. Repolarization and normal slow-wave activity resumed after 20-30 min of washout. The patch-clamp technique was used to study the block of large-conductance Ca(2+)-activated K+ channels (BK channels) by TPeA and tetraethylammonium (TEA) in excised and cell-attached patches from isolated colonic smooth muscle cells. Channel block was characterized by a voltage-dependent dissociation constant [Kd(V)] for the binding of TEA and TPeA to a blocking site located a fraction of the distance across the membrane field (delta). The extracellular TEA binding site had a Kd(0) of 0.33 mM and a delta of 0.23. The extracellular TPeA binding site had a Kd(0) of 2.2 mM but showed significantly less voltage dependence (delta = 0.02). The intracellular binding site for TEA was of low affinity [Kd(0) = 76 mM]. Intracellular TPeA was the most potent blocker of BK channel current [Kd(0) = 11.7 microM]. The voltage dependence of block by intracellular TPeA (delta = -0.21) was not significantly different from that of intracellular TEA (delta = -0.3). Internal TPeA (10 microM) also blocked a 70-pS K+ channel and a 23-pS K+ channel.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗
PubMed1998

Effects of dietary cation-anion difference on the acid-base status of dry cows.

Responses in dry matter intake (DMI) and acidbase balance to three sources of anionic salts (dietary cation-anion difference = -63 to -40 meq/kg of dry matter), an acidified fermentation by-product, MgSO4.7H2O + NH4Cl, and MgSO4.7H2O + CaCl2.2H2O + CaSO4, were evaluated relative to the responses of cows fed a control diet (dietary cationanion difference = 203 meq/kg of dry matter) that did not contain anionic salts. Diets were fed for 1-wk periods to eight nonlactating Holsteins assigned to two replicated 4 x 4 Latin squares. Daily DMI increased as time of access to the diet increased up to d 5; mean DMI over d 5 to 7 was reduced by dietary anionic salts. Diets containing anionic salts induced a mild metabolic acidosis that was completely compensated by nonrespiratory mechanisms (decreased blood bicarbonate and base excess; pCO2 and pH values were unaffected). Urinary pH values and bicarbonate excretion were reduced, and urinary NH4+ and titratable acidity excretion were increased, for cows fed diets containing anionic salts. Strong ion difference in urine was decreased by dietary anionic salts because of the relatively greater excretions of Cl- and S2- versus Na+ and K+ by cows fed these diets. Dietary anionic salts decreased mean ruminal pH by 0.12 units, possibly because of the reduced strong ion difference of ruminal fluid. Dietary anionic salts increased mean ruminal NH3 concentration by 2.2 mM, probably because of the higher nonprotein N content of these diets. The strong negative relationship (r2 = 0.95) between urinary pH and net acid excretion by cows fed the diets containing anionic salts suggested that urinary pH measurement might be a useful tool to assess the degree of metabolic acidosis that was imposed by dietary anionic salts.

Acid-Base Equilibrium↗
PubMed1997

Stable-Isotope Analysis of a Combined Nitrification-Denitrification Sustained by Thermophilic Methanotrophs under Low-Oxygen Conditions.

To simulate growth conditions experienced by microbiota at O(inf2)-limited interfaces of organic matter in compost, an experimental system capable of maintaining dual limitations of oxygen and carbon for extended periods, i.e., a pO(inf2)-auxostat, has been used. (sup15)N tracer studies on thermophilic (53(deg)C) decomposition processes occurring in manure-straw aggregates showed the emission of dinitrogen gas from the reactor as a result of simultaneous nitrification and denitrification at low pO(inf2) values (0.1 to 2.0%, vol/vol). The N loss was confirmed by nitrogen budget studies of the system. Depending on the imposed pO(inf2), 0.6 to 1.4 mmol of N/day (i.e., 20 to 40% of input N) was emitted as N(inf2). When the pO(inf2) was raised, the rates of both nitrification and denitrification increased instantaneously, indicating that ammonia oxidation was limited by oxygen. In auxostats permanently running at pO(inf2) >= 2% (vol/vol), the free ammonium pool was almost completely oxidized and was converted to nitrite plus nitrate and N(inf2) gas. Labelling of the auxostat with [(sup13)C]carbonate was conducted to reveal whether nitrification was of autotrophic or heterotrophic origin. Incorporation of (sup13)CO(inf2) into population-specific cellular compounds was evaluated by profiling the saponifiable phospholipid fatty acids (FAs) by using capillary gas chromatography and subsequently analyzing the (sup13)C/(sup12)C ratios of the individual FAs, after their combustion to CO(inf2), by isotope ratio mass spectrometry. Apart from the observed label incorporation into FAs originating from a microflora belonging to the genus Methylococcus (type X group), supporting nitrification of a methylotrophic nature, this analysis also corroborated the absence of truly autotrophic nitrifying populations. Nevertheless, the extent to which ammonia oxidation continued to exist in this thermophilic community suggested that a major energy gain could be associated with it.

Journal Article↗
PubMed1996

Ammonia-induced taurine release from cultured rabbit Müller cells is an osmoresistant process mediated by intracellular accumulation of cyclic AMP.

A previous study demonstrated the release of newly loaded radiolabelled taurine (Tau) from cultured rabbit Müller glia not only following typical cell volume-increasing treatments with high (65 mM) potassium ions or hypotonic media, but also with ammonium chloride (further referred to as ammonia), in a dose-dependent manner, at doses ranging from physiological (0.25 mM) to those accompanying hyperammonemic coma (5 mM) (Faff-Michalak et al., Glia 10:114-120, 1994). Stimulation of Tau release by ammonia, but not by 65 mM potassium, was correlated with a dose-dependent increase of intracellular cAMP levels. The release, as measured at 5 mM ammonia, was abolished by compounds that prevented cAMP increase: an adenylate cyclase inhibitor, miconazole, a protein kinase A inhibitor HA 1004, an anion channel blocker, niflumic acid, and a Tau transport site agonist, beta-alanine. The release by ammonia differed from potassium-induced release in its resistance to 1) increase of medium tonicity by addition of 50 mM sucrose; 2) addition of the anion/cation cotransport blocker, furosemide; and 3) removal of calcium from the superfusion medium. The results suggest that ammonia-induced Tau release is mediated by intracellular accumulation of cAMP and may occur either via an osmoresistant, cAMP-controlled channel or a cAMP-activated Tau transporter. The release observed at the physiological concentration of ammonium chloride suggest a role for ammonia as a signal molecule.

Ammonia↗
PubMed1976

Abnormality in metabolism of 15N-labeled nitrate in toxemia.

The urinary excretion of 15N-labeled ammonium nitrate was studied during the last few weeks in patients with normal pregnancy and in those with toxemia. Marked diminution of the 15N label was found consistently in patients with toxemia in the urinary fraction consisting of nitrogenous compounds other than urea and ammonia. The possible significance of this finding is discussed.

Adult↗
PubMed2005

Triarylborane ammonia complexes as ideal precursors for arylzinc reagents in asymmetric catalysis.

[reaction: see text] The value of arylboranes as precursors for arylzinc reagents in asymmetric catalysis is demonstrated. Kinetic studies on the transmetalation reaction with zinc reagents rationalize the observed differences of three classes of arylboranes in catalytic applications. By using the stable and easily accessible triarylborane ammonia complexes, an array of chiral diarylmethanols in high yield and enantioselectivity was synthesized.

Benzyl Alcohols↗
PubMed2003

NH(4)(+) conductance in Xenopus laevis oocytes. III. Effect of NH(3).

Exposure of Xenopus laevis oocytes to NH(4)Cl caused intracellular acidification, cell membrane depolarization and the generation of an inward current. To determine the contribution of uncharged NH(3) and positively charged NH(4)(+), the NH(4)Cl-induced inward current was measured in the presence of increasing [NH(3)] at constant [NH(4)Cl] (10 mM) or increasing [NH(4)Cl] at constant [NH(3)] (0.045 mM) with pH varying in both cases. At -70 mV, the NH(4)Cl-induced current was barely detectable at pH 6.5, 0.01 mM NH(3), but increased successively at pH 7.5, 0.1 mM NH(3) and pH 8.5, 1 mM NH(3). In contrast, NH(4)Cl-associated currents were independent of changes of the [NH(4)Cl] at constant [NH(3)] and variable pH. Similar results with respect to acidification, depolarization and inward current in response to concentration and pH changes were obtained with trimethylamine HCl. Increasing concentrations of the weak acid propionate led to a reduction of the NH(4)Cl-induced current. These data suggest that NH(3) entry may induce local alkalinization that, in turn, may trigger the opening of a conductance for NH(4)(+) or trimethylamine-H(+) entry.

Ammonia↗