Effect of 8-bromo-cAMP and dexamethasone on glutamate metabolism in rat astrocytes

Journal Article · Thu Nov 01 00:00:00 EST 1990 · Neurochemical Research; (USA)

DOI:https://doi.org/10.1007/BF01101713· OSTI ID:5642996

Zielke, H R; Tildon, J T; Landry, M E; Max, S R ^[1]

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1. Univ. of Maryland School of Medicine, Baltimore (USA)

Glutamine synthetase (GS) activity in cultured rat astrocytes was measured in extracts and compared to the intracellular rate of glutamine synthesis by intact control astrocytes or astrocytes exposed to 1 mM 8-bromo-cAMP (8Br-cAMP) + 1 microM dexamethasone (DEX) for 4 days. GS activity in extracts of astrocytes treated with 8Br-cAMP + DEX was 7.5 times greater than the activity in extracts of control astrocytes. In contrast, the intracellular rate of glutamine synthesis by intact cells increased only 2-fold, suggesting that additional intracellular effectors regulate the expression of GS activity inside the intact cell. The rate of glutamine synthesis by astrocytes was 4.3 times greater in MEM than in HEPES buffered Hank's salts. Synthesis of glutamine by intact astrocytes cultured in MEM was independent of the external glutamine or ammonia concentrations but was increased by higher extracellular glutamate concentrations. In studies with intact astrocytes 80% of the original (U-{sup 14}C)glutamate was recovered in the medium as radioactive glutamine, 2-3% as aspartate, and 7% as glutamate after 2 hours for both control and treated astrocytes. The results suggest: (1) astrocytes are highly efficient in the conversion of glutamate to glutamine; (2) induction of GS activity increases the rate of glutamate conversion to glutamine by astrocytes and the rate of glutamine release into the medium; (3) endogenous intracellular regulators of GS activity control the flux of glutamate through this enzymatic reaction; and (4) the composition of the medium alters the rate of glutamine synthesis from external glutamate.

• OSTI ID: 5642996
• Journal Information: Neurochemical Research; (USA), Vol. 15:11; ISSN 0364-3190
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
AMP
BIOCHEMICAL REACTION KINETICS
DEXAMETHASONE
GLUTAMIC ACID
METABOLISM
LIGASES
ENZYME ACTIVITY
CARBON 14 COMPOUNDS
NERVE CELLS
RATS
TRACER TECHNIQUES
ADRENAL HORMONES
AMINO ACIDS
ANIMAL CELLS
ANIMALS
CARBON COMPOUNDS
CARBOXYLIC ACIDS
CORTICOSTEROIDS
ENZYMES
GLUCOCORTICOIDS
HORMONES
HYDROXY COMPOUNDS
ISOTOPE APPLICATIONS
KETONES
KINETICS
LABELLED COMPOUNDS
MAMMALS
NUCLEOTIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
PREGNANES
REACTION KINETICS
RODENTS
SOMATIC CELLS
STEROIDS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques
550501 - Metabolism- Tracer Techniques