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METABOLIC COMPARTMENTATION OF GLUTAMATE ASSOCIATED WITH THE FORMATION OF γ‐AMINOBUTYRATE
Author(s) -
Pael. A. J.,
Johnson A. L.,
Balaazs R.
Publication year - 1974
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1974.tb12227.x
Subject(s) - glutamate receptor , compartment (ship) , citric acid cycle , amino acid , chemistry , glutamic acid , metabolism , in vivo , biochemistry , biology , medicine , endocrinology , oceanography , receptor , microbiology and biotechnology , geology
— The distibution of 14 C in the brains of rats that had been given [U‐ 14 C]glucose (10μCi/100g body wt.) at 10 min before death was followed for 20 min post mortem. The results indicated that the input of glucose‐carbon into the tricarboxylic acid cycle stopped instantaneously after death. Although the proportion (more than 40 per cent) of tissue‐ 14 C combined in the amino acids associated with the cycle did not change significantly, there was a characteristic redistribution of 14 C within the amino acid fraction after death: significantly, the 14 C content of glutamate decreased andthat of GABA increased. The GABA/glutamate specific radioactivity ratio which in vivo was 0‐58, increased progressively in the first 5 min after death, reaching a value of 0‐93. However, by 5 min the rise in the ratio stopped abruptly, although GABA accumulation continued at about half the initial rate beyond that time. These results indicated that GA BA formation is compartmented in the brain andpermitted the evaluation of certain kinetic parameters of the two compartments which could be distinguished under the experimental conditions. One of the compartments was evidently a summation of a number of subcompartments which had certain features in common, such as a low GABA flux relative to the amount of glutamate. The properties of the other compartment were compatible with those of nerve terminals functioning with GABA as the transmitter. This compartment contained about 2 per cent of the total glutamate, but the glutamate pool was labelled about three times more than the average. Further, this compartment accounted for about 50 per cent of the total GABA formation flux andcontained GABA in high concentrations (the probable values were about seven times the mean).