title: 1H nuclear magnetic resonance spectroscopy study of cerebral glutamate in an ex vivo brain preparation of guinea pig.
abstract: Cerebral glutamate was monitored in a superfused cerebral cortical preparation by 1H NMR spectroscopy using a semiselective spin-echo sequence N-acetyl aspartate (NAA) as an internal concentration reference. During controlled metabolic conditions, the cerebral 1H NMR-detected glutamate-to-NAA ratio was approximately 20-30% lower than expected from the ratio of neutralized perchloric acid extracts of the preparations. Inhibition of respiration in the presence of glucose did not change the 1H NMR glutamate-to-NAA ratio in brain slice preparation. In contrast, either complete depletion of ATP during cyanide poisoning together with 0 mM glucose, anoxia in the absence of glucose, or treatment with nigericin or with a protonophore, carbonyl cyanide-m-fluorophenylhydrazone, increased 1H NMR-detected glutamate/NAA in the cerebral preparations without a change in the relative and absolute concentration ratios determined from the tissue acid extracts. Spin-spin relaxation times of glutamate and NAA peaks in anoxic slices were 749 +/- 89 and 729 +/- 94 ms, respectively, and thus, the portion of glutamate that could not be detected by 1H NMR was quantified in absolute terms. It was calculated that an increase in the glutamate-to-NAA ratio from 0.55 +/- 0.02 to 0.67 +/- 0.02 during aglycemic anoxia corresponded to some 6 mmol/kg of tissue dry weight of glutamate from the total concentration of 28 mmol/kg dry weight. It is suggested that this 22% of total glutamate pool is present in a noncytoplasmic compartment during controlled metabolic state.
authors.affiliation: Department of Biochemistry and Biotechnology, A. I. Virtanen Institute, University of Kuopio, Finland.
authors.forename: T R
authors.initials: TR
authors.lastname: Pirttilä
authors.forename: J M
authors.initials: JM
authors.lastname: Hakumäki
authors.forename: R A
authors.initials: RA
authors.lastname: Kauppinen
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D004734:Energy Metabolism; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009550:Nigericin / Q000494:pharmacology; D010100:Oxygen / Q000494:pharmacology; D012966:Sodium Cyanide / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D005971:Glutamates; D007773:Lactates; D001224:Aspartic Acid; D019344:Lactic Acid; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; C000179:N-acetylaspartate; D012966:Sodium Cyanide; D009550:Nigericin; D010100:Oxygen