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At least 1,225 records · Page 68Linked to original sources
PubMed1989

Alterations in the microenvironment during spreading depression associated with epileptiform activity in the immature neocortex.

Local changes in extracellular ion concentrations were measured with ion-sensitive microelectrodes in slices of mature (greater than 40 days of age) or immature (16-30 days of age) rat neocortex maintained in vitro. Repetitive stimulation resulted in increases in extracellular potassium ([K+]o) to levels of 8.85 +/- 2.1 mM in slices from adult animals and 12.77 +/- 1.8 mM in slices from immature animals. During exposure to picrotoxin, maximum levels were 11.3 +/- 2.6 and 14.8 +/- 2.5 mM in the mature and immature groups, respectively. Picrotoxin (50 microM) induced spontaneous bursts of repetitive spiking, followed by a slow, negative field potential, associated with spreading depression (SD), in slices from immature animals. [K+]o levels increased to 10.2 +/- 3.9 mM during repetitive spike discharges and reached 30.3 +/- 18.5 mM during SDs. Variations in the size of the extracellular space (ES) were examined during SD. The ES was found to reversibly decrease by 39 +/- 4.5%. Clusters of repetitive spikes were associated with 0.1-0.2 mM decreases in [Ca2+]o, whereas 1.12 +/- 0.06 mM decreases were observed during SDs. Decreases in [Na+]o and [Cl-]o of 56 +/- 10 mM and 41 +/- 9 mM, respectively, were observed during SDs suggesting that a net transmembrane movement of water occurred during SDs. These results indicate that changes in [K+]o associated with epileptiform activity in the immature nervous system are quantitatively different from those observed in the mature brain. These large increases in [K+]o may contribute to the prolonged nature of epileptiform discharges in the developing nervous system.

Aging↗
PubMed1989

Thymic microenvironment in myasthenia gravis.

This study was undertaken to investigate the role of thymic epithelial (TE) cells in the immunopathology of myasthenia gravis (MG). Seventeen thymuses from patients with MG and six normal thymuses were investigated by light and electron microscopy, using a stereologic method. In the myasthenic thymuses the cortex was markedly reduced, while the medulla was hypertrophied and had numerous germinal centers. A subpopulation of cortical TE cells showed a large fibrillar nucleolus and a decreased number of cytoplasmic dense bodies and cysts, indicating decreased function. Medullary TE cells, on the other hand, showed evidence of increased activity with an enlarged euchromatic nucleus and an increased number of cytoplasmic dense bodies. There was a statistically significant negative correlation between the decrease in size of the thymic cortex and the appearance of medullary germinal centers. A significant correlation was also demonstrated between atrophy of cortical TE cells and depletion of cortical thymocytes. Our study shows that both cortical and medullary TE cells are involved in the pathogenesis of MG but have different roles.

Adult↗
PubMed1983

1H-NMR study on the tautomerism of the imidazole ring of histidine residues. II. Microenvironments of histidine-12 and histidine-119 of bovine pancreatic ribonuclease A.

The NMR titration curves of proton chemical shifts were observed for the C2 protons of histidine residues in intact bovine pancreatic RNAase A (EC 3.1.27.5) and carboxyalkylated RNAase A. By comparing the methyl region of NMR spectra, the 250-340 nm region of circular dichoic spectra, and the NMR titration curves of tyrosine ring protons among intact and modified RNAase A, it was ascertained that the carboxyalkylation of histidine residues at position 12 or 119 did not make any appreciable conformational changes to RNAase A. With the pK values determined for intact and modified RNAase A, the microscopic pK values and molar ratios of tautomers were estimated for His-12 and His-119 by means of the procedure described in the preceding paper. The estimated microscopic pK values of tautomers were 6.2 for the N1-H tautomer of His-12, more than 8 for the N3-H tautomer of His-12, 7.0 for the N1-H tautomer of His-119, and 6.4 for the N3-H tautomer of His-119, respectively. These values were interpreted in terms of the microscopic environments surrounding the histidine residues. The microscopic structure estimated in the present study was discussed, comparing it with those from X-ray crystallography and hydrogen-tritium (or hydrogen-deuterium) exchange technique.

Animals↗
PubMed1986

Microenvironment around the essential cysteine residues in chicken liver fructose-1,6-bisphosphatase as analyzed by ESR spin labelling.

Chemical modification and electron spin resonance spectroscopy (ESR) spin-labelling techniques have been employed to investigate the local environment of the essential sulfhydryl groups of chicken liver fructose-1,6-bisphosphatase. The results demonstrate the presence of two distinct classes of sulfhydryl groups in this enzyme. The first class react preferentially with iodoacetate and its spin-labelled derivative, and this results in an increase in catalytic activity, while the second class react preferentially with N-ethylmaleimide and its spin-labelled derivative, and this leads to a decrease in catalytic activity. The ESR spectral data strongly suggest that the first class of sulfhydryl groups are located in a deep cleft of the enzyme molecule, while the second class of sulfhydryl groups are located in a shallow crevice. The environment of the second class of the sulfhydryl groups appears to undergo a significant change after the modification of the first class of sulfhydryl groups by iodoacetate.

Animals↗
PubMed1988

Interaction of spin-labeled tryptamine with monoamine oxidase: probing the microenvironment of the active site by spin probe-spin label techniques.

The spin-labeled substrate, tryptamine, was used as a structural probe of the active site of bovine liver monoamine oxidase B (amine:oxygen oxidoreductase (deaminating) (flavin-containing), EC 1.4.3.4). When the reaction was monitored by electron spin resonance (ESR), line broadening effects indicative of binding with an apparent relation to substrate specificity of the highly purified enzyme were observed. The spectrum indicated that the bound tryptamine was 'partially immobilized' with a dissociation constant of 39 microM and 2.2 mol bound per enzyme dimer. The correlation time, reflecting the environment of the tryptamine binding site, was determined to be 6.2 ns. The topology of the active site was investigated by using dual spin-label methodology in which the spin-labeled substrate, tryptamine, and the 15N-substituted and deuterated maleimide spin label covalently bound to the essential sulfhydryl groups were used. The ESR spectral data suggested that the essential sulfhydryl groups are at least 14 A away from the tryptamine-binding site. The environment surrounding both spin-labeled substrates, tryptamine and [2H,15N]MSL, and the motional properties of the enzyme are discussed.

Binding Sites↗
PubMed1988

Interaction of spin-labeled tryptophan with sickle hemoglobin: probing the microenvironment of the contact sites by spin-probe--spin-label techniques.

The spin-labeled tryptophan was used as a structural probe of hemoglobin contact sites. The ESR spectral data indicated that the probe exhibits weak binding to hemoglobin with a dissociation constant of 3.2.10(-5) and 4.0 mol bound per hemoglobin tetramer. The spectrum suggested that the bound tryptophan was 'partially immobilized' with a correlation time reflecting the environment of the tryptophan binding site of 8.2 ns. The topology of the contact sites was investigated by using dual spin-label methodology in which spin-labeled tryptophan and (2H,15N) substituted and deuterated maleimide spin label [2H-15N]MSL covalently-bound to Cys-beta 93 residue were used. The ESR spectral data suggested that the tryptophan binding sites were located within 8-10 A of the nitroxide free radical of spin-labeled hemoglobin. The environment of the contact sites is discussed.

Cysteine↗
PubMed1991

Tailoring the microenvironment of enzymes in water-poor systems.

Biocatalytic systems using enzymes in organic solvents open up the possibility of performing a whole range of reactions which would not normally occur under physiological conditions. The ability to perform reverse hydrolysis, or to convert substances relatively insoluble in aqueous environments on a scale of practical value in commercial applications are among those reactions for which water-poor systems are appropriate.

Emulsions↗
PubMed1988

Sodium-coupled sugar and amino acid transport in an acidic microenvironment.

1. Nutrient transport mechanisms of lobster hepatopancreatic epithelial brush border membrane vesicles (BBMV) are strongly influenced by the acidic nature of the tubular lumen. 2. Sodium-dependent glucose uptake by BBMV was electrogenic and was stimulated at low pH by reducing sugar transport Ki, without affecting JM. 3. Glutamate was largely transported in zwitterionic form at pH 4.0 by an electrically silent cotransport mechanism with both Na and Cl. 4. Increased H+ concentration tripled the apparent membrane permeability to glutamate as well as the amino acid transport JM. 5. At pH 4.0 leucine was transported as a cation by two dissimilar carrier systems: a Na-independent process shared by polar amino acids, and an electroneutral Na-2Cl-dependent mechanism shared with non-polar amino acids. 6. A model is proposed for hepatopancreatic BBMV at acidic pH which employs ionic chemical gradients and membrane potential as nutrient transport driving forces.

Amino Acids↗
PubMed1987

The dendrites of single brain-stem motoneurons intracellularly labelled with horseradish peroxidase in the cat. An ultrastructural analysis of the synaptic covering and the microenvironment.

Two laryngeal motoneurons intracellularly stained with horseradish peroxidase were studied ultrastructurally. The precise position of the ultrastructural observations made along the dendrites was obtained from the computer-reconstruction of the motoneurons in three dimensions. The shape and the size of the synaptic boutons, the percentage of membrane covered by bouton appositions and active zones, the number of boutons per 100 microns2 (packing density) were analysed on the soma and on the labelled dendrites at different distances from the soma up to 1000 microns. The results revealed no important regional differences in the mean length of synaptic apposition. The packing density was in the range of 9.3-14.9 boutons per 100 microns2 and was not correlated with the distance from the soma. The percentage apposition covering was higher on the soma and the proximal part of the dendrites than on the remaining part of the dendritic arborization. Close appositions between labelled dendrite and unlabelled somata and/or dendrites together with dendro-dendritic synapses suggested the possibility that the dendrites may be involved in local cell-to-cell communication. Microdendrites emerging from the soma or the proximal dendrites were contacted by synaptic boutons which may be more efficient as revealed by computation.

Animals↗
PubMed1992

Regulation of transient dopamine concentration gradients in the microenvironment surrounding nerve terminals in the rat striatum.

Synaptic overflow of dopamine in the striatum has been investigated during electrical stimulation of the medial forebrain bundle in anesthetized rats. Dopamine has been detected with Nafion-coated, carbon-fiber electrodes used with fast-scan voltammetry. In accordance with previous results, dopamine synaptic overflow is a function of the stimulation frequency and the anatomical position of the carbon-fiber electrode. In some positions the concentration of dopamine is found to respond instantaneously to the stimulus when the time-delay for diffusion through the Nafion film is accounted for. In these locations the measured rates of change of dopamine are sufficiently rapid such that extracellular diffusion is not apparent. The rate of dopamine overflow can be described by a model in which each stimulus pulse causes instantaneous release, and cellular uptake decreases the concentration between stimulus pulses. Uptake is found to be described by a constant set of Michaelis-Menten kinetics at each location for concentrations of dopamine from 100 nM to 15 microM. The concentration of dopamine released per stimulus pulse is found to be greatest at low frequency (< or = 10 Hz) with stimulus trains, and with single-pulse stimulations in nomifensine-treated animals. The frequency dependence of release is not an effect of dopamine receptor activation; haloperidol (2.5 mg/kg) causes a uniform increase in release at all frequencies. The absence of diffusional effects in the measurement locations means that the constants determined with the electrode are those operant inside intact striatal tissue during stimulated overflow. These values are then extrapolated to the case where a single neuron fires alone. The extrapolation shows that while the transient concentration of dopamine may be high (200 nM) at the interface of the synapse and the extrasynaptic region, it is normally very low (< 6 nM) in the bulk of extracellular fluid.

Animals↗
PubMed1982

Residual injury to the hemopoietic microenvironment following sequential radiation and busulfan.

Our earlier studies in mice showed that sequential radiation and cyclophosphamide suppressed marrow stromal cells (MSC) and prevented local hemopoietic repopulation for several months. Because others have shown that busulfan administration caused marrow aplasia, we studied its ability, combined with radiation, to produce a persistent microenvironmental defect in mice. Intraperitoneal administration of four weekly doses of 20 mg/kg busulfan, starting one week after 1500 rad leg irradiation, produced a severe microenvironmental lesion for 6 months reflected by lack of repopulation in femoral marrow to greater than 50% of normal by MSC, hemopoietic stem cells (CFU-S), and granulocyte-macrophage precursors. Differential marrow cell counts revealed that precursors of hemopoietic cells were more profoundly affected than their progeny. Hemopoietic stem cells and MSC failed to recover in busulfan-treated mice at 6 months to the same extent as those treated with cyclophosphamide. In addition, the busulfan-treated mice had an excessive number of myeloid blast cells and a severe erythroid depletion suggesting that these animals were preleukemic. We conclude that: 1) sequential radiation and busulfan administration caused long-term microenvironmental damage reflected by incomplete repopulation of the femoral marrow and suppression of MSC, and 2) multiple courses of busulfan prevented hemopoietic repopulation longer than a similar regimen of cyclophosphamide.

Animals↗
PubMedDate not supplied

Amino acids in the neuronal microenvironment of focal human epileptic lesions.

Extracellular fluid was topically sampled with a dialysis probe during electrocorticography from the exposed cerebral cortex in 23 patients undergoing epilepsy surgery. Sampling was done in parallel from epileptiform regions and from non-epileptic areas. The former were classified according to the histopathology, into neoplastic, non-tumoral or 'special cases'. The epileptiform regions had significantly higher extracellular concentrations of alanine, glycine and phosphoethanolamine in the majority of the cases. The excised epileptic lesions were analyzed to provide the corresponding intracellular concentrations of amino acids. Several of the non-tumoral group showed high concentrations of GABA, ethanolamine and alanine. The intra- to extracellular concentration ratio for amino acids was low for phosphoethanolamine, glycine, serine and glutamine in most of the samples of epileptiform cortex, while the intracellular accumulative ability for ethanolamine apparently was stronger in epileptiform than in normal cortex.

Adolescent↗