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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    European journal of neuroscience 4 (1992), S. 0 
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The elucidation of the mechanisms regulating the properties of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) subtype of glutamate receptors is important for understanding glutamatergic transmission. Here we report that qualitative as well as quantitative analysis of tritiated ligand binding to the AMPA receptor on thin frozen rat brain tissue sections reveals the existence of several mechanisms regulating the binding properties of AMPA receptors. Preincubation of tissue sections at 35°C results in a decreased amount of [3H]AMPA binding as compared to that measured following preincubation at 0°C. The decrease in binding appears to be mainly localized to cell bodies as evaluated by autoradiography, and could be due to proteolysis. Preincubation with calcium at 35°C produces increased levels of [3H]AMPA binding. The effect of calcium is mimicked by manganese and to a lesser extent by magnesium; it is concentration-dependent with a 50% effective concentration for calcium of ∼150 μM, time-dependent and temperature-dependent. The calcium-induced increase in [3H]AMPA binding is different among various brain structures, being larger in area CA1 of the hippocampus and in the superficial layers of the cerebral cortex. The effect of calcium is partly reduced by preincubation with the calpain inhibitor leupeptin and potentiated by preincubation with purified calpain II. The calcium-induced increase in [3H]AMPA binding is associated with a decrease in the binding of an antagonist of AMPA receptors, [3H]6-nitro-7-cyanoquinoxaline-2,3-dione. The results indicate that the binding properties of the AMPA receptor are rapidly regulated by calcium-dependent processes, and possibly by calcium-dependent proteases. They suggest that modulation of the binding properties involves changes in the configuration of the receptor, producing opposite changes in the affinities of the receptor for agonists and antagonists. Finally, these results strengthen the hypothesis that changes in the properties of AMPA receptors might underlie various forms of synaptic plasticity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Changes in the activity of pyruvate dehydrogenase [pyruvate: lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1, PDH], elicited by inhibition of the phosphorylation of its 40,000 Mrα-subunit, were compared with changes in pyruvate-supported calcium accumulation by rat brain mitochondria. Dichloroacetate (DCA) produces concentration-dependent inhibition of the phosphorylation of intramitochondrial PDH a-subunit, which is accompanied by stimulation of PDH activity and calcium accumulation. DCA did not affect succinate- or ATP-supported mitochondrial calcium accumulation. The concentration of DCA giving half-maximal inhibition of the phosphorylation was almost identical to that giving half-maximal stimulation of PDH activity and calcium accumulation. PDH activity and pyruvate-supported calcium accumulation showed similar dependence on pyruvate concentration with respective apparent affinities for pyruvate of 40 μm and 30 μm, and both activities exhibited positive cooperativity. DCA modified only the maximal activity of PDH or the maximal calcium accumulation without changing either the apparent affinities for pyruvate or calcium or the Hill coefficients. These data provide evidence that calcium accumulation by mitochondria is tightly linked to PDH activity and that changes in the phosphorylation of the PDH α-subunit can be reflected in changes in the calcium-buffering ability of mitochondria. This suggests a possible mechanism by which a variety of manipulations, such as repetitive synaptic stimulation, can alter the regulation of internal calcium levels.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1612-1112
    Keywords: Capillary electrophoresis ; Anions ; System peaks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This study deals with the simultaneous analysis of UV-transparent anions by capillary electrophoresis with indirect UV-detection. With a background electrolyte (BGE) based on UV-absorbing chromate and UV-transparent borate, the interference of system peaks with those of sample anions (chloride, sulfate, citrate, phosphate) is shown. The existence of such system peaks, and their position in relation to the peaks of the sample anions, are explained on the basis of the eigenpeak theory proposed by Poppe [1]. With this BGE the system peaks were manifested as a negative peak followed by a positive peak. Their shapes depended on the relative mobilities of the analyte and BGE anions and their areas depended on the amount of sample. The mobility of the system peak depends on the borate/boric acid mobility, which was adjusted by slight variation of the pH close to its pK a-pH is the key factor governing system-peak mobility. When the locations of the system peaks are optimized, the quantification of citrate can be achieved; this was successfully used for determination of anions in milk.
    Type of Medium: Electronic Resource
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