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  • 1
    Electronic Resource
    Electronic Resource
    Acute Effect of Ammonia on Branched-Chain Amino Acid Oxidation and Incorporation into Proteins in Astrocytes and in Neurons in Primary Cultures (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 49 (1987), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: 14CO2 production and incorporation of label into proteins from the labeled branched-chain amino acids, leucine, valine, and isoleucine, were determined in primary cultures of neurons and of undifferentiated and differentiated astrocytes from mouse cerebral cortex in the absence and presence of 3 mMammonium chloride. Production of 14CO2 from [I-14C]leucine and [I-14C]valine was larger than 14CO3 production from [U-14C]leucine and [U-14C]valine in both astrocytes and neurons. In most cases more 14CO2 was produced in astrocytes than in neurons. Incorporation of labeled branched-chain amino acids into proteins varied with the cell type and with the amino acid. Addition of 3 mMammonium chloride greatly suppressed 14CO2 production from [I-14C]-labeIed branched chain amino acids but had little effect on 14CO2 production from [U-14C]-labeled branched-chain amino acids in astrocytes. Ammoniumion, at this concentration, suppressed the incorporation of label from all three branched-chain amino acids into proteins of astrocytes. In contrast, ammonium ion had very little effect on the metabolism (oxidation and incorporation into proteins) of these amino acids in neurons. The possible implications of these findings are discussed, especially regarding whether they signify variations in metabolic fluxes and/or in magnitudes of precursor pools.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1987.tb00955.x
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  • 2
    Electronic Resource
    Electronic Resource
    Identification, Characterization, Immunocytochemical Localization, and Developmental Changes in the Activity of Calcium/Calmodulin-Dependent Protein Kinase II in the CNS of Bombyx mori During Postembryonic Development (1998)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 70 (1998), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: In the present investigation, in vitro phosphorylation of CNS proteins of the silkworm Bombyx mori during the postembryonic development have been studied. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography of phosphorylated proteins revealed the presence of major phosphoproteins of 59/60 kDa. Based on molecular mass, calcium/calmodulin-dependent autophosphorylation, substrate specificity, KN-62 inhibition, apparent Km for ATP and syntide-2, these proteins were identified as calcium/calmodulin-dependent protein kinase II (CaM kinase II). Anti-rat CaM kinase II monoclonal antibody showed immunoreactivity with Bombyx CaM kinase II isoforms. This kinase showed a high degree of autophosphorylation in neural tissue. During postembryonic development of Bombyx, two distinct peaks of enzyme activity could be noticed, one at the late-larval and another at the late-pupal stage, which were associated with an increase in amount of the enzyme. These results suggested that the expression of CaM kinase II in the CNS of Bombyx was developmentally regulated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1998.70041644.x
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  • 3
    Electronic Resource
    Electronic Resource
    Cellular and Subcellular Branched-Chain Keto Acid Decarboxylase in Rat Brain and Its Response to Hyperammonemia (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 573 (1989), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1989.tb15035.x
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  • 4
    Electronic Resource
    Electronic Resource
    Ammonia-induced alterations in the metabolism of glutamate and aspartate in neuronal perikarya and synaptosomes of rat cerebellum (1992)
    Springer
    Metabolic brain disease 7 (1992), S. 51-61 
    Details
    ISSN: 1573-7365
    Keywords: ammonia toxicity ; glutamate ; cerebellum ; neuronal perikarya ; synaptosomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of subacute and acute doses of ammonium acetate was studied on the production of14CO2 from14C-labeled glutamate and aspartate by neuronal perikarya and synaptosomes isolated from rat cerebellum. Studies with inhibitors foraminotransferases (aminooxy acetic acid) and glutamate dehydrogenase (glutamic acid diethyl ester) indicated that transamination reactions play a major role in this process. There was a suppression in this process in hyperammonemic states. Activities of the enzymes, aspartate aminotransferase, alanine aminotransferase, glutamate dehydrogenase and glutaminase were decreased in both preparations in hyperammonemic states. Activity of glutamine synthetase was unaltered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01000441
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  • 5
    Electronic Resource
    Electronic Resource
    Glutamatergic synaptic dysfunction in hyperammonemic syndromes (1992)
    Springer
    Metabolic brain disease 7 (1992), S. 1-20 
    Details
    ISSN: 1573-7365
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01000437
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  • 6
    Electronic Resource
    Electronic Resource
    Pyruvate decarboxylation in astrocytes and in neurons in primary cultures in the presence and the absence of ammonia (1988)
    Springer
    Neurochemical research 13 (1988), S. 57-61 
    Details
    ISSN: 1573-6903
    Keywords: Ammonia ; astrocytes ; malate-aspartate shuttle ; neurons ; pyruvate oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Oxidative decarboxylation of [1-14C]pyruvate was studied in primary cultures of neurons and of astrocytes. The rate of this process, which is a measure of carbon flow into the tricarboxylic acid (TCA) cycle and which is inhibited by its end product, acetyl CoA, was determined under conditions which would either elevate or reduce the components of the malate-aspartate shuttle (MAS). Addition of aspartate (1 mM) was found to stimulate pyruvate decarboxylation in astrocytes whereas addition of glutamate (or glutamine) had no effect. Since aspartate is a precursor for extramitochondrial malate, and thus intramitochondrial oxaloacetate, whereas glutamate and glutamine are not, this suggests that an increase in oxaloacetate level stimulates TCA cycle activity. Conversely, a reduction of the glutamate content by 3 mM ammonia, which might reduce exchange between glutamate and aspartate across the mitochondrial membrane, suppressed pyruvate decarboxylation. This effect was abolished by addition of glutamate or glutamine or exposure to methionine sulfoximine (MSO). These findings suggest that impairment of MAS activity by removal of MAS constituents decreases TCA cycle activity whereas replenishment of these compounds restores the activity of the TCA cycle. No corresponding effects were observed in neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00971855
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  • 7
    Electronic Resource
    Electronic Resource
    Activities of pyruvate dehydrogenase, enzymes of citric acid cycle, and aminotransferases in the subcellular fractions of cerebral cortex in normal and hyperammonemic rats (1989)
    Springer
    Neurochemical research 14 (1989), S. 221-228 
    Details
    ISSN: 1573-6903
    Keywords: Citric acid cycle enzymes ; hyperammonemia ; cytosol ; mitochondria ; synaptosomes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Activity levels of pyruvate dehydrogenase, enzymes of citric acid cycle, aspartate and alanine aminotransferases were estimated in mitochondria, synaptosomes and cytosol isolated from brains of normal rats and those injected with acute and subacute doses of ammonium acetate. In mitochondria isolated from animals treated with acute dose of ammonium acetate, there was an elevation in the activities of pyruvate, isocitrate and succinate dehydrogenases while the activities of malate dehydrogenase (malate→oxaloacetate), aspartate and alanine aminotransferases were suppressed. In subacute conditions a similar profile of change was noticed excepting that there was an elevation in the activity of α-ketoglutarate dehydrogenase in mitochondria. In the synaptosomes isolated from animals administered with acute dose of ammonium acetate, there was an increase in the activities of pyruvate, isocitrate, α-ketoglutarate and succinate dehydrogenases while the changes in the activities of malate dehydrogenase, asparatate and alanine amino transferases were suppressed. In the subacute toxicity similar changes were observed in this fraction except that the activity of malate dehydrogenase (oxaloacetate→malate) was enhanced. In the cytosol, pyruvate dehydrogenase and other enzymes of citric acid cycle except malate dehydrogenase were enhanced in both acute and subacute ammonia toxicity though their activities are lesser than that of mitochondria. In this fraction malate dehydrogenase (oxaloacetate→malate), was enhanced while activities of malate dehydrogenase (malate→oxaloacetate), aspartate, and alanine aminotransferases were suppressed in both the conditions. Based on these results it is concluded that the decreased activities of malate dehydrogenase (malate→oxaloacetate) in mitochondria and of aspartate, aminotransferase in mitochondria and cytosol may be responsible for the disruption of malate-aspartate, shuttle in hyperammonemic state. Possible existence of a small vulnerable population of mitochondria in brain which might degenerate and liberate their contents into cytosol in hyperammonemic states is also suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00971314
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  • 8
    Electronic Resource
    Electronic Resource
    Isolation of astrocytes, neurons, and synaptosomes of rat brain cortex (1985)
    Springer
    Neurochemical research 10 (1985), S. 239-250 
    Details
    ISSN: 1573-6903
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract A simplified method was developed for the bulk separation of neuronal perikarya and astroglial celis from adult rat brain without the involvement of density gradients. Activities of various enzymes involved in glutamate metabolism were estimated and compared with those of synaptosomes. The activities of glutamate dehydrogenase and aspartate aminotransferase were higher in synaptosomes than in neuronal perikarya or glia. Glutamine synthetase was distributed in all the three fractions while glutaminase activity was higher in astrocytes than in synaptosomes and was not detectable in neuronal perikarya. The significance of these results in relation to metabolic compartmentation was discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00964570
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  • 9
    Electronic Resource
    Electronic Resource
    Differential effects of ammonia and β-methylene-dl-aspartate on metabolism of glutamate and related amino acids by astrocytes and neurons in primary culture (1989)
    Springer
    Neurochemical research 14 (1989), S. 377-389 
    Details
    ISSN: 1573-6903
    Keywords: Glutamate metabolism ; astrocytes ; neurons ; effects of ammonia and β-methylene-dl-aspartate ; aspartate aminotransferase ; malate-aspartate shuttle ; aspartate ; glutamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effects of ammonium chloride (3 mM) and β-methylene-dl-aspartate (BMA; 5 mM) (an inhibitor of aspartate aminotransferase, a key enzyme of the malate-aspartate shuttle (MAS)) on the metabolism of glutamate and related amino acids were studied in primary cultures of astrocytes and neurons. Both ammonia and BMA inhibited14CO2 production from [U-14C]-and [1-14C]glutamate by astrocytes and neurons and their effects were partially additive. Acute treatment of astrocytes with ammonia (but not BMA) increased astrocytic glutamine. Acute treatment of astrocytes with ammonia or BMA decreased astrocytic glutamate and aspartate (both are key components of the MAS). Acute treatment of neurons with ammonia decreased neuronal aspartate and glutamine and did not apparently affect the efflux of aspartate from neurons. However, acute BMA treatment of neurons led to decreased neuronal glutamate and glutamine and apparently reduced the efflux of aspartate and glutamine from neurons. The data are consistent with the notion that both ammonia and BMA may inhibit the MAS although BMA may also directly inhibit cellular glutamate uptake. Additionally, these results also suggest that ammonia and BMA exert differential effects on astroglial and neuronal glutamate metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01000042
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  • 10
    Electronic Resource
    Electronic Resource
    Uptake and metabolism of glutamate and aspartate by astroglial and neuronal preparations of rat cerebellum (1993)
    Springer
    Neurochemical research 18 (1993), S. 647-654 
    Details
    ISSN: 1573-6903
    Keywords: Glutamate ; aspartate ; astrocytes ; neurons ; synaptosomes ; uptake ; CO2 production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Astrocytes, neuronal perikarya and synaptosomes were prepared from rat cerebellum. Kinetics of high and low affinity uptake systems of glutamate and aspartate, nominal rates of14CO2 production from [U−14C]glutamate, [U−14C]aspartate and [1−14C]glutamate and activities of enzymes of glutamate metabolism were studied in these preparations. The rate of uptake and the nomial rate of production of14CO2 from these amino acids was higher in the astroglia than neuronal perikarya and synaptosomes. Activities of glutamine synthetase and glutamate dehydrogenase were higher in astrocytes than in neuronal perikarya and synaptosomes. Activities of glutaminase and glutamic acid decarboxylase were observed to be highest in neuronal perikarya and synaptosomes respectively. These results are in agreement with the postulates of theory of metabolic compartmentation of glutamate while others (presence of glutaminase in astrocytes and glutamine synthetase in synaptosomes) are not. Results of this study also indicated that (i) at high extracellular concentrations, glutamate/aspartate uptake may be predominantly into astrocytes while at low extracellular concentrations, it would be into neurons (ii) production of α-ketoglutarate from glutamate is chiefly by way of transamination but not by oxidative deamination in these three preparations and (iii) there are topographical differences glutamate metabolism within the neurons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00966777
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