PubMed Health⌕ Search

Biomedical subjects

L Peng

Publications and source records attributed to L Peng.

At least 127 records · Page 7Linked to original sources
PubMed1994

High extracellular potassium concentrations stimulate oxidative metabolism in a glutamatergic neuronal culture and glycolysis in cultured astrocytes but have no stimulatory effect in a GABAergic neuronal culture.

Rates of deoxyglucose accumulation and of CO2 production from [U-14C]glucose, or from [U-14C]lactate or [2-14C]pyruvate (as a determination of tricarboxylic acid (TCA) cycle activity) were determined in primary cultures of either astrocytes, cerebellar granule cell neurons (utilizing glutamate as their transmitter) or cerebral cortical interneurons (utilizing GABA as their transmitter) during control ('resting') conditions and during exposure to an elevated extracellular potassium concentration, mimicking functional activity. The elevation of the extracellular potassium concentration increased the rate of deoxyglucose accumulation, but not of TCA cycle activity in astrocytes and both deoxyglucose accumulation and TCA cycle activity in cerebellar granule cells, but had no stimulatory effect in cerebral cortical neurons. Based on these observations it is suggested that the increase in energy metabolism in the CNS in vivo during functional activity mainly reflects increased active accumulation of potassium ions and extrusion of sodium ions in neurons receiving excitatory input and in adjacent astrocytes in order to re-establish pre-stimulus ion distribution across cell membranes.

Animals↗
PubMed1994

Photochemical labeling of membrane-associated and channel-forming domains of proteins directed by energy transfer.

Singlet-singlet energy transfer reactions from excited tryptophan residues to photoactivatable probes possessing a suitable chromophore, generate reactive species in the vicinity of the protein, leading to its covalent labeling. This delayed labeling process can be used to map the membrane-surrounded regions of proteins with improved efficiency when it is applied with appropriate photoactivatable phospholipids. The same principle could also be applied to the labeling of channel-forming transmembrane domains of ion channels, provided that suitable photoactivatable permeant ions were available. Both applications will be discussed with regard to their potential and feasibility.

Affinity Labels↗
PubMed1994

Alteration in oxidative metabolism of alanine in cerebellar granule cell cultures as a consequence of the development of the ability to utilize alanine as an amino group donor for synthesis of transmitter glutamate.

Formation of 14CO2 from labeled alanine was measured in cultured cerebellar granule cells grown in the combined presence of alanine, alpha-ketoglutarate and glutamine or in the presence of glutamine alone. This was done in order to study whether the utilization of alpha-ketoglutarate plus alanine as precursors of transmitter glutamate, induced by culturing in the presence of these compounds, is reflected by an increase of CO2 production from alanine during stimulation with an elevated extracellular potassium concentration. Potassium stimulated CO2 production from alanine was present only in the cells grown in the combined presence of alanine, alpha-ketoglutarate and glutamine. This stimulation was abolished by glutamine, but not by ouabain, indicating that the depolarizing-induced stimulation of alanine metabolism is a consequence of increased release of transmitter glutamate formed from alanine, not a simple result of an increased metabolic rate.

Alanine↗
PubMed1994

Cell death in primary cultures of mouse neurons and astrocytes during exposure to and 'recovery' from hypoxia, substrate deprivation and simulated ischemia.

Effects of hypoxia, substrate deprivation and simulated ischemia (combined hypoxia and substrate deprivation) on cell survival during the insult itself and during a 24 h 'recovery' period were studied in primary cultures of mouse astrocytes and in cerebral cortical neuronal-astrocytic co-cultures. Cell death was determined by release of the cytosolic high molecular enzyme lactate dehydrogenase (LDH) as well as morphologically (retention of staining with rhodamine 123 and lack of staining with propidium iodide as an indicator of live cells). Glutamate concentrations were measured in the incubation media at the end of the metabolic insults. Astrocytes were very resistant to hypoxia, but less so to simulated ischemia; under both conditions the glutamate concentrations in the media remained low. Cerebral cortical neurons were almost equally susceptible to damage by hypoxia and by simulated ischemia, although hypoxia had a faster deleterious effects on some of the neurons and simulated ischemia during a long-term insult (9 h) killed all neurons, whereas a non-negligible neuronal subpopulation survived 9 h of hypoxia. Neuronal cell death after long-term hypoxia (but not after simulated ischemia) was correlated with high concentrations of glutamate in the incubation media. After certain insults, most notably relatively short lasting simulated ischemia (3 h) in neurons (which caused no increased cell death during the insult), there was a large release of LDH during the 'recovery' period.

Analysis of Variance↗
PubMed1994

Plasma interleukin-1 alpha and beta, tumor necrosis factor-alpha, and lipopolysaccharide concentrations during pulmonary exacerbations of cystic fibrosis.

Earlier studies have reported the presence of interleukin-1 (IL-1) and tumor necrosis factor (TNF) in the plasma of patients with cystic fibrosis (CF), but the results have been inconsistent. To investigate the relationships among plasma IL-1 alpha, IL-1 beta, TNF, lipopolysaccharide (LPS), and clinical status, measurements were made before and after 14 days of intravenous antibiotic therapy in 13 patients with CF. In addition, whole blood cytokine production rates were measured in 18 hr cultures stimulated with 10 micrograms/mL LPS or sterile saline (control). On admission, patients with CF had significantly greater plasma levels of LPS and IL-1 alpha compared with 20 healthy adult controls. In response to antibiotic therapy, the patients had statistically significant increases in weight, oxygen saturation, chest radiograph score, and forced expiratory volume in 1 second. They had significant decreases in pulse rate, residual volume/total lung capacity ratio, white blood count, neutrophil count, LPS concentration, and resting energy expenditure per kg body weight. There were no significant changes in the plasma concentrations of IL-1 alpha, IL-1 beta, or TNF and no significant changes in the basal or stimulated whole blood production rates of IL-1 alpha, IL-1 beta, or TNF. The immunological variables did not correlate significantly with clinical measurements of severity or the presence of fever. It is likely that in CF local pulmonary effects of cytokines are of more pathophysiologic significance than systemic effects.

Adolescent↗
PubMed1994

Molecular cloning, expression and mutagenesis of an anti-insulin single chain Fv (scFv).

The immunoglobulin variable region genes of a murine anti-insulin IgG-producing hybridoma were rescued and cloned into a bacterial expression vector. The variable regions of the gamma heavy chain and the kappa light chain were expressed independently and together as a single chain antibody (scFv). The variable heavy chain alone demonstrated the ability to bind to insulin. The kappa light chain did not show any binding activity towards insulin. The scFv was constructed by PCR assembly using a (Gly4Ser)3 linker between the carboxyl end of the variable heavy chain and the amino terminus of the kappa light chain. The scFv bound insulin at an IC50 of 3.5 x 10(-8) M whereas the parent antibody bound insulin at 1.0 x 10(-8) M. Mutagenesis of the variable heavy chain complementarity determining regions (CDR) indicated that CDR1 and CDR3 were important for binding to insulin. Position 99 in CDR3 of the heavy chain was found to be a critical position for the ability of the scFv to bind to insulin.

Amino Acid Sequence↗
PubMed1994

Uptake, release, and metabolism of citrate in neurons and astrocytes in primary cultures.

Synthesis, uptake, release, and oxidative metabolism of citrate were investigated in neurons and astrocytes cultured from cerebral cortex or cerebellum. In addition, the possible role of citrate as a donor of the carbon skeleton for biosynthesis of neurotransmitter glutamate was studied. All cell types expressed the enzyme citrate synthase at a high activity, the cerebellar granule neurons containing the enzyme at a higher activity than that found in the astrocytes from the two brain regions or the cortical neurons. Saturable citrate uptake could not be detected in any of the cell types, but the astrocytes, and, in particular, those of cerebellar origin, had a very active de novo synthesis and release of citrate (approximately 70 nmol x h-1 x mg of protein-1). The rate of release of citrate from neurons was < 5% of this value. Using [14C]citrate it could be shown that citrate was oxidatively metabolized to 14CO2 at a modest rate (approximately 1 nmol x h-1 x mg-1 of protein) with slightly higher rates in astrocytes compared with neurons. Experiments designed to investigate the ability of exogenously supplied citrate to serve as a precursor for synthesis of transmitter glutamate in cerebellar granule neurons failed to demonstrate this. Rather than citrate serving this purpose it may be suggested that astrocytically released citrate may regulate the extracellular concentration of Ca2+ and Mg2+ by chelation, thereby modulating neuronal excitability.

Animals↗
PubMed1994

Signalling effect of elevated potassium concentrations and monoamines on brain energy metabolism at the cellular level.

The effects of elevated K+ concentrations and monoamine transmitters on different cell types in the CNS and on different subcellular structures in these cells are reviewed. Pronounced differences exist in the metabolic processes that are stimulated by excess K+ and by adrenergic agonists, e.g., noradrenaline. An elevation in the extracellular K+ concentration appears to enhance neuronal-astrocytic interaction by stimulating metabolic processes involved in (1) the promotion of supply of precursors for transmitter glutamate, and (2) reestablishment of resting ion distribution following neuronal excitation. The monoamine transmitters stimulate energy production and Na+,K(+)-ATPase activity in astrocytes in a complex manner and, in so doing, facilitate their role in ion regulation. However, in contrast to excess K+, they do not enhance the production of astrocytic precursors for neuronal glutamate production. Emphasis is placed on possible profound differences in metabolic effects on excitatory and inhibitory neurotransmission and on the importance of stimulation of glycolytic metabolism in astrocytes versus oxidative metabolism in neurons.

Animals↗
PubMed1994

Distribution of red cell blood group systems in Achang and De'ang ethnic groups in China.

A survey on the distribution of red cell group systems, including ABO, MNSs, Rhesus and P, was carried out in the Achang and De'ang ethnic groups in Yunnan Province, South-West China. The Achangs are characterized by the highest frequency of IA in China, while the De'angs show a high frequency of IO and CDe. The distribution of these blood group systems in Achang and De'ang exhibits the same characteristics observed in other ethnic groups of South China.

ABO Blood-Group System↗
PubMed1993

Potassium-induced stimulation of oxidative metabolism of glucose in cultures of intact cerebellar granule cells but not in corresponding cells with dendritic degeneration.

Production of 14CO2 from uniformly labelled glucose was measured in conventional cultures of mouse cerebellar granule cells (a glutamatergic cell type) and in corresponding cultures which had been grown in such a manner that they showed massive degeneration of dendrites, but were otherwise morphologically normal. Both kind of cultures were studied during exposure to either a physiological potassium concentration (5 mM) or an elevated extracellular potassium concentration. During exposure to the normal extracellular potassium concentration, the rate of CO2 production in the two types of culture was identical. In the conventional granule cell cultures, the CO2 production showed a rectilinear increase as a function of the extracellular potassium concentration from 5-100 mM; this stimulation was abolished by ouabain, a specific inhibitor of Na+,K(+)-ATPase. In granule cells showing dendritic degeneration, CO2 production increased only slightly at extracellular potassium concentrations of 25-100 mM. These findings suggest that the metabolic stimulation in morphologically intact cells may be the result of a depolarization-induced sodium uptake, which has a mainly or exclusively dendritic localization, and secondarily leads to a stimulation of the Na+,K(+)-ATPase at its intracellular sodium-sensitive site.

Animals↗
PubMed1993

Stimulation of glycogenolysis in astrocytes by fluoxetine, an antidepressant acting like 5-HT.

Fluoxetine is a recently introduced, widely used antidepressant. It is known as a specific inhibitor of serotonin uptake into synaptosomes but has not previously been recognized as having any direct effect on brain cell serotonin receptors. The present study describes direct effects of fluoxetine on free cytosolic calcium concentration and on breakdown of glycogen in astrocytes (a glial cell type), which are known to express serotonin receptors. Evidence is presented, suggesting that these effects are evoked by an agonist action on the 5-HT1C receptor.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Uptake, release, and metabolism of alanine in neurons and astrocytes in primary cultures.

The uptake, release, and metabolism of alanine were studied in primary cultures of cerebral cortical neurons or astrocytes and cerebellar granule neurons. All three cell types exhibited a saturable, sodium-dependent uptake of alanine with Km values (microM) of 256 +/- 30, 463 +/- 39, and 292 +/- 39, respectively, and Vmax values (nmol/min/mg) of 15.9 +/- 0.7, 7.9 +/- 0.01, and 17.4 +/- 0.8, respectively. The corresponding values (nmol/min/mg) for the specific activity of alanine aminotransferase were 4.7 +/- 0.4, 17.1 +/- 2.5, and 4.5 +/- 0.9 (all values represent the mean +/- SEM). Release of alanine from the cells was rectilinear with time over a 10 hr period in case of astrocytes (40 nmol/hr/mg) and cerebellar granule neurons (21 nmol/hr/mg). In cortical neurons the release rate declined from an initial value of 19 nmol/hr/mg during the first 3 hr to a value of less than 3 nmol/hr/mg during the subsequent 7 hr of incubation. Metabolism of [14C]alanine to 14CO2 was found to have a lag period of 15 min and subsequently the rate of CO2 production was constant over a 45 min period with a value of 0.5 nmol/min/mg in granule neurons and about 0.3 nmol/min/mg in the other two cell types. Altogether the results show that alanine is preferentially produced in and released from astrocytes and accumulated into both GABAergic cortical neurons and glutamatergic cerebellar granule neurons.

Aging↗
PubMed1993

Glutamate effects on calcium homeostasis in cerebellar granule cells in primary cultures grown under depolarizing and nondepolarizing conditions.

Cerebellar granule cell cultures are normally grown under partly depolarizing conditions (in a medium with approximately 25 mM K+), but these cultures can also be grown at a normal potassium concentration (5.4 mM K+), although some of their characteristics are altered. In this study, intracellular free calcium concentration and 45Ca uptake were measured in cerebellar granule cell cultures grown at either 25 or 5.4 mM extracellular potassium in the presence of glutamate, and/or some of its subtype-specific agonists and antagonists. Granule cells in cultures grown at 25 mM K+ responded to glutamate, but not to quisqualate, with an increase in free cytosolic calcium concentration and in 45Ca uptake. This increase in free cytosolic calcium concentration was dependent on extracellular calcium and it was antagonized by AP5 and ketamine, NMDA receptor antagonists. In contrast, granule cells in cultures grown at 5.4 mM K+ responded to both glutamate and quisqualate, and these responses were independent of extracellular calcium and not sensitive to AP5 and ketamine. In agreement with this, 45Ca uptake was not affected by glutamate. Neither of the two culture types responded to kainate with an increase in calcium concentration or uptake. These observations indicate that calcium uptake in granule cells in cultures grown at 25 mM K+ reflect NMDA activation of calcium influx, whereas the cells in cultures grown at 5 mM K+ increase cytosolic calcium concentration on account of intracellular release of bound calcium, caused by activation of the metabotropic receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1993

Lymphocyte B and T cell subsets in peripheral blood from patients with asbestosis.

Peripheral blood lymphocytes were analysed by indirect staphylococcus protein A (SPA) rosette assay using monoclonal antibodies that identify B cells, total T cells (OKT3+), helper-inducer T cells (OKT4+), and suppressor-cytotoxic T cells (OKT8+). The purpose of this investigation was to determine the characteristics of lymphocyte B and T subsets in peripheral blood, and the relation of the changes to radiographic abnormalities in workers exposed to asbestos.

Adult↗
PubMed1993

Glutamate and glutamine metabolism and compartmentation in astrocytes.

Metabolism of glutamate and glutamine in cultured mouse cerebral cortical astrocytes has been investigated using either radioactively labelled (14C) amino acids or 13C-labelled amino acids combined with NMR spectroscopy of cell extracts and lyophilyzed incubation media. Using [U-13C]glutamate it has been shown that in astrocytes exogenously supplied glutamate is primarily (70%) metabolized oxidatively through the tricarboxylic acid (TCA) cycle and to a lesser extent (30%) directly to glutamine. Glutamate metabolized in the TCA cycle is to a large extent recovered as lactate showing that the astrocyte-specific enzyme, malic enzyme is functionally active. Incubation with [U-14C]glutamine led to a higher specific radioactivity in glutamate than in glutamine. It could also be shown that glutamate and glutamine were metabolized differently to aspartate and alanine. These results taken together strongly suggest that glutamate/glutamine metabolism in astrocytes is compartmentalized and a model with multiple cytoplasmic and mitochondrial compartments of these amino acids is proposed.

Animals↗
PubMed1993

Utilization of glutamine and of TCA cycle constituents as precursors for transmitter glutamate and GABA.

In the present review evidence is presented that (1) glutamine synthesis in astrocytes is essential for synthesis of GABA in neurons; (2) alpha-ketoglutarate in the presence of alanine (as an amino group donor) can replace glutamine as a precursor for synthesis of transmitter glutamate, but maybe not as a precursor for transmitter GABA; (3) differences exist in the intraneuronal metabolic pathways for utilization of alpha-ketoglutarate plus alanine and of glutamine, and (4) alanine also functions as a substrate for oxidative metabolism in glutamatergic neurons. It should be emphasized that the supply of precursors for transmitter glutamate and GABA in glutamatergic and GABAergic neurons depends on metabolic processes in astrocytes regardless whether glutamine or alpha-ketoglutarate plus L-alanine function as the transmitter precursors. The key reason that an interaction with astrocytes is essential is that both pyruvate carboxylase, the major enzyme in the brain for net synthesis of tricarboxylic acid cycle intermediates, and glutamine synthetase, the enzyme forming glutamine from glutamate, are specifically located in astrocytes, but not in neurons.

Animals↗
PubMed1993

Comparison of amino acid sequences of the trypsin inhibitors from taro (Colocasia esculenta), giant taro (Alocasia macrorrhiza) and giant swamp taro (Cyrtosperma chamissonis).

The amino acid sequences of the trypsin inhibitors from taro Colocasia esculenta var. esculenta and giant swamp taro Cyrtosperma chamissonis have been determined and are compared with the protein sequence of the trypsin/chymotrypsin inhibitor from giant taro Alocasia macrorrhiza. Both inhibitors display polymorphism and there is evidence of two components in the giant swamp taro. The positional identity between the proteins is highest at 73-75% for the comparison of the giant taro (GT) with the polymorphic forms of the taro (T) inhibitors and lowest at 56-58% for the pairs of taro and giant swamp taro (GST) proteins. The comparisons show that the inhibitors from T and GT are more related to each other than to GST, which supports their taxonomic classification into different tribes. Location of the P1 site for the trypsin inhibitors of aroids is different from that of other Kunitz-type inhibitors and could be at Leu56.

Amino Acid Sequence↗