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Glucose and glutamine metabolism in rat thymocytes.

ABSTRACT: The metabolism of glucose and glutamine in freshly prepared resting and concanavalin A-stimulated rat thymocytes was studied. Concanavalin A addition enhanced uptake of both glucose and glutamine and led to an increase in oxidative degradation of both substrates to CO2. With variously labelled [14C]glucose, it was shown that the pathways of glucose dissimilation were equally stimulated by the mitogen. A disproportionately large percentage of the extra glucose taken up was converted into lactate, but concanavalin A also caused an increase in the oxidation of pyruvate as judged by the enhanced release of 14CO2 from [2-14C]-, [3,4-14C]- and [6-14C]-glucose. Addition of glutamine did not affect glucose metabolism. The major end products of glutamine metabolism by resting and mitogen-stimulated rat thymocytes were glutamate, aspartate, CO2 and NH3. Virtually no lactate was formed from glutamine. Concanavalin A enhanced the formation of all end products except glutamate, indicating that more glutamine was metabolized beyond the stage of glutamate in the mitogen-activated cells. Addition of glucose caused a significant decrease in the rates of glutamine utilization and conversion into aspartate and CO2 in the absence and in the presence of concanavalin A. In the presence of glucose, almost all nitrogen of the metabolized glutamine was accounted for as NH3 released via the glutaminase and/or glutamate dehydrogenase reactions. In the absence of glucose, part (18%) of the glutamine nitrogen was metabolized by the resting and to a larger extent (38%) by the mitogen-stimulated thymocytes via a transaminase or amidotransferase reaction.

SUBMITTER: Brand K

PROVIDER: S-EPMC1144061 | biostudies-other | 1984 Jul

REPOSITORIES: biostudies-other

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Project description:Energy metabolism in proliferating cultured rat thymocytes was compared with that of freshly prepared non-proliferating resting cells. Cultured rat thymocytes enter a proliferative cycle after stimulation by concanavalin A and Lymphocult T (interleukin-2), with maximal rates of DNA synthesis at 60 h. Compared with incubated resting thymocytes, glucose metabolism by incubated proliferating thymocytes was 53-fold increased; 90% of the amount of glucose utilized was converted into lactate, whereas resting cells metabolized only 56% to lactate. However, the latter oxidized 27% of glucose to CO2, as opposed to 1.1% by the proliferating cells. Activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and aldolase in proliferating thymocytes were increased 12-, 17-, 30- and 24-fold respectively, whereas the rate of pyruvate oxidation was enhanced only 3-fold. The relatively low capacity of pyruvate degradation in proliferating thymocytes might be the reason for almost complete conversion of glucose into lactate by these cells. Glutamine utilization by rat thymocytes was 8-fold increased during proliferation. The major end products of glutamine metabolism are glutamate, aspartate, CO2 and ammonia. A complete recovery of glutamine carbon and nitrogen in the products was obtained. The amount of glutamate formed by phosphate-dependent glutaminase which entered the citric acid cycle was enhanced 5-fold in the proliferating cells: 76% was converted into 2-oxoglutarate by aspartate aminotransferase, present in high activity, and the remaining 24% by glutamate dehydrogenase. With resting cells the same percentages were obtained (75 and 25). Maximal activities of glutaminase, glutamate dehydrogenase and aspartate aminotransferase were increased 3-, 12- and 6-fold respectively in proliferating cells; 32% of the glutamate metabolized in the citric acid cycle was recovered in CO2 and 61% in aspartate. In resting cells this proportion was 41% and 59% and in mitogen-stimulated cells 39% and 65% respectively. Addition of glucose (4 mM) or malate (2 mM) strongly decreased the rates of glutamine utilization and glutamate conversion into 2-oxoglutarate by proliferating thymocytes and also affected the pathways of further glutamate metabolism. Addition of 2 mM-pyruvate did not alter the rate of glutamine utilization by proliferating thymocytes, but decreased the rate of metabolism beyond the stage of glutamate significantly. Formation of acetyl-CoA in the presence of pyruvate might explain the relatively enhanced oxidation of glutamate to CO2 (56%) by proliferating thymocytes.

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Glucose and glutamine metabolism in rat thymocytes.

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