High glucose stimulates glutamate uptakes in pancreatic beta-cells / 한국실험동물학회지

Pancreatic beta-cells are major cells responsible for glucose metabolism in the body. Hyperglycemia is known to be a primary factor in the induction of diabetes mellitus. Glutamate is also an excitatory neurotransmitter in diverse organs. Oxidative stress also plays a pivotal role in the development of diabetes mellitus. However, the effect of hyperglycemia in glutamate uptake in the pancreas is not clear. Furthermore, the relationship between high glucose-induced glutamate uptake and oxidative stress has not been investigated. Therefore, this study was conducted to investigate the effect of high glucose on glutamate uptake in pancreatic beta-cells. In the present study, 25 mM glucose stimulated the glutamate uptake in HIT-15 cells of hamster pancreatic beta-cells. The treatment of 25 mM glucose and 1 mM glutamate also decreased the cell viability in HIT-15 cells. In addition, the treatment of 25 mM glucose induced an increase of lipid peroxide formation. High glucose-induced increase of LPO formation was prevented by the treatment of antioxidants such as N-acetyl-L-cysteine and quercetin. Furthermore, high glucose-induced stimulation of glutamate uptake and decrease of cell viability were also blocked by the treatment of N-acetyl-L-cysteine and quercetin. In conclusion, high glucose stimulated glutamate uptake via oxidative stress in pancreatic beta-cells.

Group Ⅱ and Ⅲ metabotropic glutamate receptors agonists reverse 1-methyl-4-phenylpyridinium-induced glutamate uptake inhibition in C6 glioma cells / 中国临床药理学与治疗学

AIM: To study the effect of group Ⅱ and Ⅲ metabotropic glutamate receptors (mGluRs) agonists on 1-methyl-4-phenylpyridinium (MPP~+)-induced glutamate uptake inhibition in C6 glioma cells. METHODS: The glutamate uptake into astrocytes was measured by using radio-ligand binding assay method. RESULTS: It was shown that Group Ⅱ mGluRs agonist (2' S, 2' R, 3 ' R) -2- (2', 3 ' -dicarboxycyclopropyl) glycine (DCG-Ⅳ) (100 ?mol?L~(-1)) and Group Ⅲ mGluRs agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4) (100 ?mol?L~(-1)) significantly reversed MPP~+-induced glutamate uptake inhibition. Furthermore, the enhancement effects of DCG-Ⅳ and L-AP4 were blocked by their respective antagonists, (RS)-1 -Amino-5-phosphonoinan-1-carboxylic acid (APICA) and (RS)-?-methylserine-O-phosphate (MSOP). CONCLUSION: Group Ⅱ and Ⅲ mGluRs agonists produce neuroprotective effects by enhancing the activity of glutamate transporters.

Group Ⅱ and Ⅲ metabotropic glutamate receptors agonists reverse 1-methyl-4-phenylpyridinium -induced glutamate uptake inhibition / 中国临床药理学与治疗学

AIM: To study the effects of group Ⅱ and Ⅲ metabotropic glutamate receptors (mGluRs) agonists on 1-methyl-4-phenylpyridinium (MPP+) -induced glutamate uptake inhibition. METHODS: The glutamate uptake into astrocytes was measured by using radio-ligand binding assay method,and the viability of astrocytes was investigated by MTT method. RESULTS: It was shown that MPP+(150, 200 ?mol?L -1 ) inhibited glutamate uptake into astrocytes,but produced no effect on the viability of astrocytes,and the inhibition rates were 58.3 % and 70.1 %,respectively. Group Ⅱ mGluRs agonist (2'S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (DCG-IV) ( 0.1 ,1,10, 100 ?mol?L -1 ) and Group Ⅲ mGluRs agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4) (1,10, 100 ?mol?L -1 ) significantly reversed MPP+-induced glutamate uptake inhibition. CONCLUSION: MPP+ directly inhibits the function of glutamate transporters,and group Ⅱ and Ⅲ mGluRs agonists produce neuroprotective effects by enhancing the activity of glutamate transporters.

Agonists of group II and III metabotropic glutamate receptors reverse LPS-induced glutamate uptake inhibition in C6 glioma cells / 中国临床药理学与治疗学

AIM: To study whether agonists of group II and III metabotropic glutamate receptors (mGluRs) exert effects on LPS-induced glutamate uptake inhibition in C6 glioma cells. METHODS: The glutamate uptake into C6 glioma cells was measured by uptake of [3H]-D,L-glutamate; and the apoptosis and the viability of C6 glioma cells were investigated by Hoechst33342 and MTT methods, respectively. RESULTS: LPS (4, 6 ?g/mL) inhibited glutamate uptake significantly compared with that in the control group without effect on the apoptosis and viability of C6 glioma cells. Pretreatment of C6 glioma cells with group II and III mGluRs agonists DCG-IV(100 ?mol/L) and L-AP4(100 ?mol/L) reversed LPS-induced glutamate uptake inhibition. These recovery effects were abolished by their respective antagonists APICA and MSOP. CONCLUSION: Activation of group II and III mGluRs recovers LPS-induced glutamate uptake inhibition in C6 glioma cells, suggesting the enhancement of glutamate uptake is involved in neuroprotective roles exerted by group II and III mGluRs agonists.

Effects of dexamethasone and DHEA on the changes of glutamate and polyamine uptake in rat astrocytes by lipopolysaccharide and antimycin A

Interactions among dexamethasone, dehydroepiandrosterone (DHEA), lipopolysaccharide (LPS), and antimycin A on the glutamate uptake and the polyamine uptake were investigated in primary cultures of rat cerebral cortical astrocytes to examine the effects of dexamethasone and DHEA on the regulatory role of astrocytes in conditions of increased extracellular concentrations of glutamate or polyamines. 1. (3H)Glutamate uptake: LPS and antimycin A decreased Vmax, but both drugs had little effect on Km. Dexamethasone also decreased basal Vmax without any significant effect on Km. And dexamethasone further decreased the antimycin A-induced decrease of Vmax. DHEA did not affect the kinetics of basal glutamate uptake and the change by LPS or antimycin A. 2. (14C)Putrescine uptake: LPS increased Vmax, and antimycin A decreased Vmax. They showed little effect on Km. Dexamethasone decreased Vmax of basal uptake and further decreased the antimycin A-induced decrease of Vmax, and also decreased Vmax to less than control in LPS-treated astrocytes. DHEA did not affect Km and the change of Vmax by LPS or antimycin A. 3. (14C)Spermine uptake: Antimycin A decreased Vmax, and LPS might increase Vmax. Km was little affected by the drugs. Dexamethasone decreased basal Vmax and might further decrease the antimycin A-induced decrease of Vmax. And dexamethasone also decreased Vmax to less than control in LPS-treated astrocytes. DHEA might increase basal Vmax and Vmax of LPS-treated astrocytes. 4. Vmax of glutamate uptake by astrocytes was increased by putrescine (1000 muM & 2000 muM) and spermidine (200 muM, 500 muM & 2000 muM). Spermine, 200 muM (and 100 muM), also increased Vmax, but a higher dose of 2000 muM decreased Vmax. Km of glutamate uptake was not significantly changed by these polyamines, except that higher doses of spermine showed tendency to decrease Km of glutamate uptake. In astrocytes, dexamethasone inhibited the glutamate uptake and the polyamine uptake in normal or hypoxic conditions, and the polyamine uptake might be stimulated by LPS and DHEA. Polyamines could aid astrocytes to uptake glutamate.

Effect of t-butylhydroperoxide on Na+/-dependent glutamate uptake in rabbit brain synaptosome

The effect of an organic peroxide, t-butylhydroperoxide (t-BHP), on glutamate uptake was studied in synaptosomes prepared from cerebral cortex. t-BHP inhibited the Na+/-dependent glutamate uptake with no change in the Na+/-independent uptake. This effect of t-BHP was not altered by addition of Ca2+ channel blockers (verapamil, diltiazem and nifedipine) or PLA2 inhibitors (dibucaine, butacaine and quinacrine). However, the effect was prevented by iron chelators (deferoxamine and phenanthroline) and phenolic antioxidants (N,N'-diphenyl-phenylenediamine, butylated hydroxyanisole, and butylated hydroxytoluene). At low concentrations (< 1.0 mM), t-BHP inhibited glutamate uptake without altering lipid peroxidation. Moreover, a large increase in lipid peroxidation by ascorbate/Fe2+ was not accompanied by an inhibition of glutamate uptake. The impairment of glutamate uptake by t-BHP was not intimately related to the change in Na+/-K+/-ATPase activity. These results suggest that inhibition of glutamate uptake by t-BHP is not totally mediated by peroxidation of membrane lipid, but is associated with direct interactions of glutamate transport proteins with t-BHP metabolites. The Ca2+ influx through Ca2+ channel or PLA2 activation may not be involved in the t-BHP inhibition of glutamate transport.

Selective inhibition of glutamate uptake by mercury in cultured mouse astrocytes

We studied the effects of organic and inorganic mercury (Hg) on the uptake of L-[3H] glutamate (L-GLU) in cultured mouse astrocytes. Following exposure to mercuric chloride (MC) [0.2 approximately 5.0 microM], selective and dose-dependent inhibition of L-GLU uptake to 50% of control levels was observed, whereas 2-deoxyglucose (2-DG) uptake was not significantly affected. Methylmercuric chloride (MMC) also inhibited L-GLU uptake but 50% reduction was reached only at a concentration of 10 microM. Inhibition of L-GLU uptake by MMC appears to be closely linked to voltage-sensitive calcium channels as evidenced by the lack of L-GLU uptake inhibition by MMC in calcium-free medium or in the presence of the channel blocker verapamil. Exposure to a variety of divalent metallic ions, including CuCl2, FeCl2 and ZnCl2, did not affect L-GLU uptake in astrocytes in vitro. Exposure to PbCl2, however, resulted in a decline in L-GLU uptake, though to a much smaller degree than that observed with Hg compounds. Selective impairment of astroglial L-GLU transport may represent a critical early pathogenetic feature of Hg-induced neurotoxicity.

Iptakalim hydrochloride enhances glutamate uptake activity in synaptosomes from rat models of Parkinsons disease / 中国药理学通报

AIM To study the relationship between the activity of glutamate transporters and Parkinson's disease (PD), examine whether a novel ATP sensitive potassium (K ATP) channel opener Iptakalim (Ipt) hydrochloride enhances glutamate uptake activity, and to investigate its mechanisms. METHODS Rats were stereotaxically injected with 6 hydroxydopamine (6 OHDA) in SNpc. The synaptosomes from normal and PD rats were isolated, and [ 3H] glutamate uptake in synaptosomes was measured by using liquid scintillation counting. RESULTS [ 3H] glutamate uptake by synaptosomes from striatum and cerebral cortex of PD rats decreased and the redution was recovered by administration with Ipt (10, 50, 100 ?mol?L -1 ). The protective effect of Ipt was blocked by co adiministration with glibenclamide (20 ?mol?L -1 ), an inhibitor of sulphonylurea receptors. CONCLUSION Our results demonstrate for the first time the protective role of K ATP channel in glutamate uptake of synaptosomes and conceptually support the view that Ipt may have potential and feasibility in therapy for PD.