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L Hertz

Publications and source records attributed to L Hertz.

At least 127 records · Page 7Linked to original sources
PubMed1988

Energy metabolism in glutamatergic neurons, GABAergic neurons and astrocytes in primary cultures.

Several aspects of energy metabolism (glucose utilization, lactate production, 14CO2 production from labeled glucose, glutamate or pyruvate, oxygen consumption and contents of ATP and phosphocreatine) were measured in cerebellar granule cells (glutamatergic) in primary cultures and compared with corresponding data for cerebral cortical neurons (mainly GABA-ergic) and astrocytes. Cerebellar granule cells and astrocytes were metabolically more active than cerebral cortical neurons. Glutamate which is utilized as a major metabolic fuel as astrocytes and, to a lesser extent, in cerebral cortical neurons, was virtually not oxidized in cerebellar granule cells.

Animals↗
PubMed1988

Evidence for involvement of the astrocytic benzodiazepine receptor in the mechanism of action of convulsant and anticonvulsant drugs.

The anticonvulsant drugs carbamazepine, phenobarbital, trimethadione, valproic acid and ethosuximide at pharmacologically relevant concentrations inhibit [3H]diazepam binding to astrocytes in primary cultures but have much less effect on a corresponding preparation of neurons. Phenytoin as well as pentobarbital (which is not used chronically as an anticonvulsant) are equipotent in the two cell types. The convulsants picrotoxinin and pentylenetetrazol, the convulsant benzodiazepine RO 5-3663 and the two convulsant barbiturates DMBB and CHEB similarly inhibit diazepam binding to astrocytes but have little effect on neurons. On the basis of these findings it is suggested that these convulsants and anticonvulsants owe at least part of their effect to an interaction with the astrocytic benzodiazepine receptor, perhaps by interference with a calcium channel.

Animals↗
PubMed1988

Effects of ammonia and beta-methylene-DL-aspartate on the oxidation of glucose and pyruvate by neurons and astrocytes in primary culture.

Both ammonia and beta-methylene-DL-aspartate (beta-MA), an irreversible inhibitor of aspartate aminotransferase activity and thus of the malate-aspartate shuttle, were found previously to decrease oxidative metabolism in cerebral cortex slices. In the present work, the possibility that ammonia and beta-MA affect energy metabolism by a common mechanism (i.e., via inhibition of the malate-aspartate shuttle) was investigated using primary cultures of neurons and astrocytes. Incubation of astrocytes for 30 min with 5 mM beta-MA resulted in a decreased production of 14CO2 from [U-14C]glucose, but did not affect 14CO2 production from [2-14C]pyruvate. Conversely, incubation of astrocytes with 3 mM ammonium chloride resulted in decreased 14CO2 production from [2-14C]pyruvate, but 14CO2 production from [U-14C]glucose was not significantly affected. Ammonium chloride had no significant effect on 14CO2 production from either [U-14C]glucose or [2-14]pyruvate by neurons. However, incubation of neurons with beta-MA or beta-MA plus ammonium chloride resulted in a approximately 45% decrease of 14CO2 production from both [U-14C]glucose and [2-14C]pyruvate. A 2-h incubation of astrocytes with beta-MA resulted in no change in ATP levels, but a 35% decrease in phosphocreatine. Similar treatment of neurons resulted in greater than 50% decrease in ATP, but had little effect on phosphocreatine. beta-MA also caused a decrease in glutamate and aspartate content of neurons, but not of astrocytes. The different metabolic responses of neurons and astrocytes towards beta-MA were probably not due to a differential inhibition of aspartate aminotransferase which was inhibited by approximately 45% in astrocytes and by approximately 55% in neurons.

Adenosine Triphosphate↗
PubMed1988

Evidence that aspartate aminotransferase activity and ketodicarboxylate carrier function are essential for biosynthesis of transmitter glutamate.

Based on the selective inhibition of glutamate release in cerebellar granule cells in primary cultures by the aspartate aminotransferase inhibitor, aminooxyacetic acid, and by the ketodicarboxylate carrier inhibitor, phenylsuccinate, a novel model for synthesis of transmitter glutamate is suggested: Glutamate is formed from glutamine in the mitochondrial intramembrane space by phosphate-activated glutaminase, transported across the inner membrane in exchange with aspartate, transaminated in the matrix to alpha-ketoglutarate, which via the ketodicarboxylate carrier is transferred to the cytoplasm, and transaminated to form transmitter glutamate. Such a mechanism would explain the functional role of aspartate aminotransferase in glutamatergic neurons.

Aminooxyacetic Acid↗
PubMed1987

Inhibition of [3H]diazepam binding in primary cultures of astrocytes by atrial natriuretic peptide and by a cyclic GMP analog.

Atrial natriuretic peptide (ANP) was found potently (IC50 = 88 nM) to inhibit [3H]diazepam binding to astrocytes in primary cultures but not to a corresponding preparation of neurons. Based upon this finding and literature data demonstrating a pronounced correlation between the distribution of 'peripheral-type' benzodiazepine receptors and ANP receptors, it is suggested that ANP may be an allosteric regulator of the astrocytic benzodiazepine binding site. Since ANP is known to increase the level of cGMP it was also investigated whether 8-bromoguanosine 3':5' cyclic monophosphate, a permeable cGMP analog, displaced diazepam binding. This was the case, suggesting that cGMP might be involved in the ANP effect on the astrocytic benzodiazepine receptor.

Animals↗
PubMed1987

Dissimilarities between benzodiazepine-binding sites and adenosine uptake sites in astrocytes and neurons in primary cultures.

The question whether the benzodiazepine receptor site in astrocytes or in neurons might be identical to the adenosine uptake site was studied by determining pharmacological profiles, inhibition types, and the effects of benzodiazepine antagonists in primary cultures of either astrocytes or neurons. Fourteen different benzodiazepines and five different adenosine uptake inhibitors displaced [3H] diazepam and inhibited adenosine uptake in both astrocytes and neurons. However, the rank orders (determined as IC50 values) with which these two parameters were affected were profoundly different, indicating dissimilarities between these two sites. For several of the compounds a difference in inhibition type (competitive vs. noncompetitive) was observed between the benzodiazepine-binding site and the adenosine uptake site in astrocytes and/or neurons, which further corroborated the conclusion of a difference between the benzodiazepine-binding site and the adenosine uptake site. Finally, the neuronal benzodiazepine antagonists RO 15-1788 and CGS-8216 and the astrocytic benzodiazepine antagonist PK 11195, which reverse the action of benzodiazepines, were not able to reverse inhibition of adenosine uptake by diazepam but exerted an inhibitory effect of their own.

Adenosine↗
PubMed1987

Comparison between acute and chronic effects of ammonia on branched-chain amino acid oxidation and incorporation into protein in primary cultures of astrocytes and of neurons.

A comparison was made of acute and chronic effects of ammonia on production of 14CO2 from the [U-14C] labeled branched-chain amino acids (BCAA) leucine, isoleucine, and valine as well as from [1-14C] leucine, and on the incorporation of radioactivity from these amino acids into a perchloric-acid-precipitable protein fraction in astrocytes and neurons in primary cultures. Acute exposure of astrocytes to 3mM ammonium chloride suppressed 14CO2 production from [U-14C] BCAA and especially from [1-14C] leucine. This inhibitory effect was abolished or even reversed [( U-14C] leucine) after chronic exposure to ammonia. Analogously, incorporation of radioactivity into the protein fraction was inhibited after acute exposure but not after chronic exposure of astrocytes to ammonia. The total protein content per culture was increased after chronic exposure. In neurons, production of 14CO2 and incorporation of 14C into proteins were less affected than in astrocytes. These results are discussed in relation to the ability of the two cell types to synthesize glutamine.

Amino Acids, Branched-Chain↗
PubMed1987

Pharmacological characteristics of diazepam receptors in neurons and astrocytes in primary cultures.

Benzodiazepine binding sites in mouse astrocytes and neurons in primary cultures were labeled with [3H]diazepam (1.8 nM), and their inhibition by 14 different benzodiazepines and 3 benzodiazepine antagonists was studied. RO 5-4864, RO 7-3351, and, especially, the antagonist PK 11195 were much more potent in astrocytes than in neurons, whereas the opposite was true for the agonists alprazolam, clonazepam, flurazepam, RO 11-3128, and chlordiazepoxide, and, especially, the antagonists CGS-8216 and RO 15-1788. Flunitrazepam, diazepam, midazolam, RO 11-6893, and RO 5-2181 were about equipotent in the two cell types. The neuronal, but not the astrocytic, binding site showed stereospecificity. In astrocytes most of the drugs had pseudo-Hill coefficients close to one, whereas the pseudo-Hill coefficients in neurons, except for RO 5-4864 and PK 11195, were distinctly lower than one. Thus, the benzodiazepine binding sites had profoundly different pharmacological characteristics in neurons and in astrocytes.

Animals↗
PubMed1987

Acute effect of ammonia on branched-chain amino acid oxidation and incorporation into proteins in astrocytes and in neurons in primary cultures.

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 mM ammonium chloride. Production of 14CO2 from [1-14C]leucine and [1-14C]valine was larger than 14CO2 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 mM ammonium chloride greatly suppressed 14CO2 production from [1-14C]-labeled branched chain amino acids but had little effect on 14CO2 production from [U-14C]-labeled branched-chain amino acids in astrocytes. Ammonium ion, 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.

Amino Acids, Branched-Chain↗
PubMed1986

Lipid and glycolipid metabolism of cultured astrocytes: a time course study.

Primary cultures of astrocytes free of neurons and containing less than 1% of oligodendrocytes were examined for their ability to incorporate labeled precursors into lipids and glycolipids. At selected developmental stages cultures were double-labeled with either [3H]glycerol and [14C]acetate or with [3H]galactose and Na2[35SO4] for a total of 72 hr. Lipids were extracted with CHCl3/CH3OH, fractionated on a silicic acid column, and further resolved by two-dimensional thin-layer chromatography. It was found that cultured astrocytes actively incorporate acetate and glycerol into various phospholipids; they have very limited ability to utilize galactose and virtually lack the synthetic machinery to use Na2SO4 for the synthesis of sulfated sphingogalactolipids; and their overall lipid metabolism is very distinct from that of oligodendrocytes. It was also found that cultured astrocytes have low levels of 2',3' cyclic phosphodiesterase and glycerol phosphate dehydrogenase activities; the latter is less than one fifth of that in oligodendrocytes.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1986

Uptake of GABA and nipecotic acid in astrocytes and neurons in primary cultures: changes in the sodium coupling ratio during differentiation.

The coupling ratio between sodium and GABA or the GABA analog, (RS)- nipecotic acid, in neuronal and glial uptake of GABA or nipecotic acid was investigated as a function of the morphological differentiation of these cell types in primary cultures. Both in neurons and astrocytes a high-affinity uptake of GABA and nipecotic acid was observed regardless of the degree of differentiation. The values of Km were essentially identical in undifferentiated and differentiated cells. On the other hand, Vmax was significantly increased both in 10-day-old neurons compared to 1- and 3-day-old neurons and in astrocytes treated with dBcAMP compared to untreated cells, i.e., Vmax increased as a function of differentiation in both cell types. In neurons as well as in astrocytes the morphological differentiation resulted in an alteration in the coupling ratio between sodium and GABA. From calculated Hill coefficients it could be deduced that the coupling ratio between sodium and GABA was changed from 1 to 2 during differentiation. Similar results were obtained for (RS)-nipecotic acid.

Animals↗
PubMed1986

Similarities of adenosine uptake systems in astrocytes and neurons in primary cultures.

Uptake of extracellular adenosine was studied in primary cultures of astrocytes or neurons. Both cell types showed a high affinity uptake. The Km values were not significantly different (6.5 +/- 3.75 microM in astrocytes and 6.1 +/- 1.86 microM in neurons), but the intensity of the uptake was higher in astrocytes than in neurons (Vmax values of 0.16 +/- 0.030 and 0.105 +/- 0.010 nmol x min-1 x mg-1 protein, respectively). The temperature sensitivity was similar in the two cell types. Adenosine uptake inhibitors and benzodiazepines inhibited the adenosine uptake systems in both astrocytes and neurons with IC50 values in the high nanomolar or the micromolar range and the rank order of potency was similar in the two cell types. In both cell types the (-) isomers of two sets of benzodiazepine stereoisomers were more potent than the (+) isomers. Dixon analysis showed that dipyridamole, papaverine, hexobendine and chlordiazepoxide inhibited the adenosine uptake competitively and clonazepam noncompetitively in both cell types.

Adenosine↗
PubMed1986

Effects of barbiturates on energy metabolism by cultured astrocytes and neurons in the presence of normal and elevated concentrations of potassium.

Rates of consumption of oxygen and of the formation of CO2 from [U-14C]glucose were studied in primary cultures of either astrocytes or neurons of the cerebral cortex. An increase of the extracellular concentration of potassium from 5 to 55 mM caused an increase in uptake of oxygen and in the production of CO2 in the astrocytes but not in the neurons. Pentobarbital (0.25-1.0 mM) or phenobarbital (1 mM) abolished the stimulation of oxygen uptake and/or the production of CO2 produced by potassium in the astrocytes with less (CO2 production) or no (oxygen uptake) effect at a normal concentration of potassium. In the neurons, pentobarbital (0.1-1.0 mM) caused, in contrast, a moderate inhibition of the production of CO2 and uptake of oxygen which was at least as pronounced at the small concentration of potassium. These results suggest that the pronounced inhibition of the stimulation of uptake of oxygen induced by potassium in brain slices is exerted on astrocytes, whereas the more modest decrease in uptake of oxygen at a small concentration of potassium is a neuronal phenomenon.

Animals↗
PubMed1986

Non-linear kinetics of glutamyl-tRNA synthesis catalyzed by high molecular weight complexes from rat brain neuronal cells but not from glial cells.

High molecular weight complexes of aminoacyl-tRNA synthetases isolated from rat brain catalyze the formation of glutamyl-tRNA with an initial lag time of the order of 1 min, as previously reported for the formation of glutamyl-tRNA and glutaminyl-tRNA catalyzed by similar complexes from bovine brain (Vadeboncoeur and Lapointe, Eur. J. Biochem., 109 (1980) 581-587). To determine the type(s) of brain cell(s) where this phenomenon occurs, we have studied the kinetics of glutamyl-tRNA formation catalyzed by high molecular weight complexes of aminoacyl-tRNA synthetases isolated from neuronal and from glial cells, either transformed (Neuro-2A and C6), or from primary cultures, or isolated from rat brain. The delay in the formation of glutamyl-tRNA was observed only in the case of neuronal cells isolated from rat brain, whereas a delay in the formation of glutaminyl-tRNA was also seen in these cells, as well as in neuronal cells in primary culture and in synaptosomes. The kinetics of formation of aspartyl-tRNA and valyl-tRNA catalyzed by high molecular weight complexes from all these cells was linear.

Acylation↗
PubMed1985

Binding of [3H]Ro 5-4864 in primary cultures of astrocytes.

Intact primary cultures of astrocytes display benzodiazepine receptors, which can be labeled with [3H]Ro 5-4864. Binding of [3H]Ro 5-4864 is specific, saturable and temperature dependent, being maximal at 0 degrees C. Scatchard analyses show a single population of high affinity binding sites with a Kd value of 6.7 nM and a Bmax value of congruent to 12,000 fmol/mg protein. The binding reaches equilibrium at congruent to 100 min, with k+1 of 0.0078 nM-1 X min-1 and is rapidly reversible with k-1 of 0.057 min-1. [3H]Ro 5-4864 binding is not modulated by GABA. Certain benzodiazepines (flunitrazepam, diazepam, Ro 7-3351) and dipyridamole displace this binding with IC50 values in the nanomolar range, whereas other benzodiazepines (alprazolam, clonazepam, chlordiazepoxide) as well as carbamazepine, phenytoin and phenobarbital have IC50 values in the micromolar range. These characteristics resemble those of Ro 5-4864 binding to brain membrane preparations reported by other authors and thus indicate that the cultured astrocytes are good models of their in vivo counterparts.

Animals↗