Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Plasma membrane potential generated by Na+, K(+)-ATPase provides the driving force for high-affinity, Na(+)-dependent uptake of glutamate into the cytoplasm of glutamatergic nerve endings and glial cells. Ca2(+)-calmodulin-dependent ATPase in the plasma membrane and Ca2(+)-ATPase in the endoplasmic reticulum influence the intracellular [Ca2+] and, therefore, the exocytotic release of neurotransmitter glutamate. The membrane potential across the membrane of the synaptic vesicles, generated by a H(+)-ATPase, provides the driving force for synaptic vesicular uptake of glutamate as well as that of GABA and glycine. Hypoxia and ischemia lead to release of glutamate, perhaps in consequence of an increased endogenous pool of glutamate and/or lack of substrate (ATP) for the ATPases. This release, rather than being exocytotic, is believed to result mainly from a reversal of the Na(+)-dependent high-affinity glutamate transporter in the plasma membrane.
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PMID:Interrelationship between glutamate and membrane-bound ATPases in nerve cells. 198 May 85

Perturbations of the synaptic handling of glutamate have been implicated in the pathogenesis of brain damage after transient ischemia. Notably, the ischemic episode is associated with an increased extracellular level of glutamate and an impaired metabolism of this amino acid in glial cells. Glutamate uptake is reduced during ischemia due to breakdown of the electrochemical ion gradients across neuronal and glial membranes. We have investigated, in the rat hippocampus, whether an ischemic event additionally causes a reduced expression of the glial glutamate transporter GLT1 (Pines et al. 1992) in the postischemic phase. Quantitative immunoblotting, using antibodies recognizing GLT1, revealed a 20% decrease in the hippocampal contents of the transporter protein, 6 h after an ischemic period lasting 20 min induced by four vessel occlusion. In situ hybridization histochemistry with 35S labelled oligonucleotide probes or digoxigenin labelled riboprobes directed to GLT1 mRNA showed a decreased signal in the hippocampus, particularly in CA1. This reduction was more pronounced at 3 h than at 24 h after the ischemic event. We conclude that the levels of GLT1 mRNA and protein show a modest decrease in the postischemic phase. This could contribute to the delayed neuronal death typically seen in the hippocampal formation after transient ischemia.
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PMID:Reduced postischemic expression of a glial glutamate transporter, GLT1, in the rat hippocampus. 761 37

In the present investigation we studied the synaptosomal uptake of glutamate in brain omogenate of Mongolian gerbils submitted to bilateral common carotid occlusion, with and without subsequent return of blood flow. The results show that glutamate uptake after ischemia is reduced by about 35%. The damage appears to be persistent, since return of blood flow restores uptake only slightly. The membrane alterations occurring in ischemia could explain the persistence of glutamate transporter impairment. Besides the blockade of NMDA receptors, the stimulation and/or the protection of the uptake systems for glutamate could be of help in preventing neuronal ischemic damage.
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PMID:Synaptosomal glutamate uptake in a model of experimental cerebral ischemia. 778 43

Arachidonic acid has been proposed to be a messenger molecule released following synaptic activation of glutamate receptors and during ischemia. Here we demonstrate that micromolar levels of arachidonic acid inhibit glutamate uptake mediated by EAAT1, a human excitatory amino acid transporter widely expressed in brain and cerebellum, by reducing the maximal transport rate approximately 30%. In contrast, arachidonic acid increased transport mediated by EAAT2, a subtype abundantly expressed in forebrain and midbrain, by causing the apparent affinity for glutamate to increase more than 2-fold. The results demonstrate that the response of different glutamate transporter subtypes to arachidonic acid could influence synaptic transmission and modulate excitotoxicity via positive or negative feedback according to the transporter(s) present in a particular region.
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PMID:Differential modulation of human glutamate transporter subtypes by arachidonic acid. 789 76

The potent antioxidant activity of carvedilol could explain part of its protective action in brain ischemia, and interaction as a low-affinity non-competitive (uncompetitive) antagonist of the N-methyl-D-aspartate (NMDA) receptor would provide rapid channel blockade at this subtype of glutamate receptor. We have now found carvedilol to be neuroprotective (PC50 = 306 nM) against 40 microM veratridine which kills cerebellar granule cell neurons in 60 min regardless of energy state. Carvedilol was also a potent inhibitor (IC50 = 1.7 microM) of veratridine-stimulated 3[H]aspartate release from preloaded neurons, caused by reversal of the Na(+)-dependent glutamate transporter. Veratridine caused a sustained 4.3-fold increase in intracellular Ca2+ ([Ca2+]i) up to 368 nM (n = 22). Carvedilol reversed the [Ca2+]i levels by a maximum of 73% with an IC50 of 0.9 microM. Such reversal of [Ca2+]i was facilitated by Na+/Ca2+ exchange since the stoichiometry of exchange could be disrupted by prior treatment with 1 microM ouabain to inhibit the Na+/K+ pump. These data suggest that, in addition to its antihypertensive effects, antioxidant activity and ability to act as a non-competitive inhibitor at the NMDA receptor, carvedilol has additional neuroprotective activity as a Na+ channel modulator and glutamate release inhibitor.
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PMID:Neuroprotective effects of carvedilol, a new antihypertensive, as a Na+ channel modulator and glutamate transport inhibitor. 791 41

Changes in the functioning of the glutamatergic system in rabbit brain were studied after partial brain ischemia and reperfusion. In vitro studies were conducted relating to the release of L-[14C]glutamate from cortical brain slices, L-[14C]glutamate uptake in synaptosomes, and 45Ca uptake in synaptosomes. It was found that basal release of L-[14C]glutamate from rabbit brain cortical slices after 30 min of partial ischemia and 1 d of reperfusion was essentially without change compared to the control values. After 3 d of reperfusion, there was an increase in basal release of L-[14C]glutamate from rabbit brain cortical slices. K+ stimulated release of L-[14C]glutamate in normal Krebs-Ringer medium was essentially the same in the control group and in the experimental group after 30 min of ischemia. The K+ stimulated release of L-[14C]glutamate independent of calcium was increased to 145% after 30 min of ischemia and 1 d of reperfusion. The decreased Km value at the glutamate transporter may have contributed to this difference. Kinetic parameters of the L-[14C]glutamate uptake (Km and Vmax) in synaptosomes from rabbit brain were significantly lower after 30 min of ischemia. The authors discovered that during the reperfusion period, Vmax was almost the same as in the control group. The activity of the Na+/Ca2+ exchanger in synaptosomes of rat brain was about 70% of the control values after 30 min of ischemia and 72 h of reperfusion. According to our results, increased L-[14C]glutamate release after 30 min of ischemia appears to be the result of higher intracellular calcium concentration and possibly also of a higher uptake of glutamate.
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PMID:Transport mechanism of L-[14C]glutamate in cortical slices and synaptosomes of rabbits exposed to brain ischemia and reperfusion. 853 15

The mouse gene encoding glial high-affinity, Na+-dependent glutamate transporter Slc1a3 (GluT-1/GLAST) was isolated, and its structural organization was characterized. The gene appeared to exist as a single copy in the mouse genome and comprised 10 exons spanning more than 56 kilobases. The transcription initiation sites were mapped to positions 503, which is the first transcriptional point (defined as +1), 128 (+376), and 64 (+440) basepairs upstream of the 3'-end of exon 1 by primer extension. The 5'-flanking region of the mouse GluT-1 gene had a typical CCAAT box and a GC box but lacked a TATA box. These features of the promoter region were characteristic of housekeeping genes. The fusion plasmids containing approximately 4 kb of the 5'-flanking region (-3830 to +450) and the firefly luciferase gene induced a significant luciferase activity when transfected into COS-1 cells. Distal deletion of the 5'-flanking region, leaving 619 bp (-169 to +450), resulted in a marked decrease in luciferase activity in COS-1 cells, suggesting that a CCAAT box, which was positioned at -200, is necessary for the expression of this gene. In situ hybridization localized this gene to mouse chromosome 15A2. These structural features will lead to a better understanding of the regulatory mechanism of the expression of the GluT-1 gene by ischemia and will also provide a basis for future evolutionary comparisons with other neurotransmitter transporters.
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PMID:Genomic organization, promoter analysis, and chromosomal localization of the gene for the mouse glial high-affinity glutamate transporter Slc1a3. 866 Oct 10

There are significant Ca2+-independent increases in extracellular glutamate and aspartate during various CNS insults such as ischemia and anoxia. However, the cellular sources of such presumed nonvesicular excitatory amino acid (EAA) release have not been established. To further explore potential mechanisms and sites for EAA release, we studied the release of preloaded [3H]-D-aspartate from primary cultured astrocytes prepared from the cerebral cortices of rat pups. Two phases of release were seen in response to raised KCl. The first phase was small and transient, and the second phase was slower and increased progressively. The initial phase of [3H]-D-aspartate release was greatly enhanced by ouabain pretreatment and was inhibited when astrocytes were preexposed to the EAA transport inhibitor threo-hydroxy beta-aspartic acid (THBA). Neither of these manipulations affected the second release component. The second phase of release was inhibited by an anion channel blocker, L-644,711, which is known to inhibit hypotonic swelling-induced release of EAA. Ouabain also resulted in the first phase of release occurring at lower [K+]o. Omission of Ca2+ had no effect on either phase of [3H]-D-aspartate release. These results support the hypothesis that the first component of release in cultured astrocytes is a reversal of the glutamate transporter, and the second component is a result of high KCl-induced swelling. Because marked increases in [K+]o are well established in CNS pathologies such as ischemia, such release may represent a significant source for the increased extracellular EAAs seen in such conditions.
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PMID:Release of [3H]-D-aspartate from primary astrocyte cultures in response to raised external potassium. 898 8

The postsynaptic actions of glutamate are rapidly terminated by high affinity glutamate uptake into glial cells. In this study we demonstrate the stimulation of both glutamate uptake and Na,K-ATPase activity in rat astrocyte cultures in response to sublethal ischemia-like insults. Primary cultures of neonatal rat cortical astrocytes were subjected to hypoxia, or to serum- and glucose-free medium, or to both conditions (ischemia). Cell death was assessed by propidium iodide staining of cell nuclei. To measure sodium pump activity and glutamate uptake, 3H-glutamate and 86Rb were both simultaneously added to the cell culture in the presence or absence of 2 mM ouabain. Na,K-ATPase activity was defined as ouabain-sensitive 86Rb uptake. Concomitant transient increases (2-3 times above control levels) of both Na,K-ATPase and glutamate transporter activities were observed in astrocytes after 4-24 h of hypoxia, 4 h of glucose deprivation, and 2-4 h of ischemia. A 24 h ischemia caused a profound loss of both activities in parallel with significant cell death. The addition of 5 mM glucose to the cells after 4 h ischemia prevented the loss of both sodium pump activity and glutamate uptake and rescued astrocytes from death observed at the end of 24 h ischemia. Reoxygenation after the 4 h ischemic event caused the selective inhibition of Na,K-ATPase activity. The observed increases in Na,K-ATPase activity and glutamate uptake in cultured astrocytes subjected to sublethal ischemia-like insults may model an important functional response of astrocytes in vivo by which they attempt to maintain ion and glutamate homeostasis under restricted energy and oxygen supply.
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PMID:Stimulation of glutamate uptake and Na,K-ATPase activity in rat astrocytes exposed to ischemia-like insults. 903 29

Dopamine can form reactive oxygen species and other reactive metabolites that can modify proteins and other cellular constituents. In this study, we tested the effect of dopamine oxidation products, other generators of reactive oxygen species, and a sulfhydryl modifier on the function of glutamate transporter proteins. We also compared any effects with those on the dopamine transporter, a protein whose function we had previously shown to be inhibited by dopamine oxidation. Preincubation with the generators of reactive oxygen species, ascorbate (0.85 mM) or xanthine (500 microM) plus xanthine oxidase (25 mU/ml), inhibited the uptake of [3H]glutamate (10 microM) into rat striatal synaptosomes (-54 and -74%, respectively). The sulfhydryl-modifying agent N-ethylmaleimide (50-500 microM) also led to a dose-dependent inhibition of [3H]glutamate uptake. Preincubation with dopamine (100 microM) under oxidizing conditions inhibited [3H]glutamate uptake by 25%. Exposure of synaptosomes to increasing amounts of dopamine quinone by enzymatically oxidizing dopamine with tyrosinase (2-50 U/ml) further inhibited [3H]glutamate uptake, an effect prevented by the addition of glutathione. The effects of free radical generators and dopamine oxidation on [3H]glutamate uptake were similar to the effects on [3H]dopamine uptake (250 nM). Our findings suggest that reactive oxygen species and dopamine oxidation products can modify glutamate transport function, which may have implications for neurodegenerative processes such as ischemia, methamphetamine-induced toxicity, and Parkinson's disease.
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PMID:Inhibition of glutamate transport in synaptosomes by dopamine oxidation and reactive oxygen species. 928 42


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