Excitatory amino acid-stimulated uptake of /sup 22/Na+ in primary astrocyte cultures
In this study we have found that L-glutamic acid, as well as being taken up by a Na+-dependent mechanism, will stimulate the uptake of 22Na+ by primary astrocyte cultures from rat brain in the presence of ouabain. By simultaneously measuring the uptake of 22Na+ and L-3H-glutamate a stoichiometry of 2-3 Na+ per glutamate was measured, implying electrogenic uptake. Increasing the medium K+ concentration to depolarize the cells inhibited L-3H-glutamate uptake, while calculations of the energetics of the observed L-3H-glutamate accumulation also supported an electrogenic mechanism of at least 2 Na+:1 glutamate. In contrast, kinetic analysis of the Na+ dependence of L-3H-glutamate uptake indicated a stoichiometry of Na+ to glutamate of 1:1, but further analysis showed that the stoichiometry cannot be resolved by purely kinetic studies. Studies with glutamate analogs, however, showed that kainic acid was a very effective stimulant of 22Na+ uptake, but 3H-kainic acid showed no Na+ -dependent uptake. Furthermore, while L-3H-glutamate uptake was very sensitive to lowered temperatures, glutamate-stimulated 22Na+ uptake was relatively insensitive. These results indicate that glutamate-stimulated uptake of 22Na+ in primary astrocytes cultures cannot be explained solely by cotransport of Na+ with glutamate, and they suggest that direct kainic acid-type receptor induced stimulation of Na+ uptake also occurs. Since both receptor and uptake effects involve transport of Na+, accurate measurements of the Na+ :glutamate stoichiometry for uptake can only be done using completely specific inhibitors of these 2 systems.
- Research Organization:
- Albany Medical College, Albany, NY (USA)
- OSTI ID:
- 6258041
- Journal Information:
- J. Neurosci.; (United States), Vol. 9:4
- Country of Publication:
- United States
- Language:
- English
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AMINO ACIDS
BIOCHEMICAL REACTION KINETICS
SODIUM COMPOUNDS
UPTAKE
ANIMAL CELLS
BRAIN
CATIONS
CELL CULTURES
GLUTAMIC ACID
MEMBRANE TRANSPORT
NERVE CELLS
OUABAIN
POTASSIUM
RATS
SODIUM 22
STOICHIOMETRY
TRACER TECHNIQUES
TRITIUM COMPOUNDS
ALKALI METAL COMPOUNDS
ALKALI METAL ISOTOPES
ALKALI METALS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BODY
CARBOHYDRATES
CARBOXYLIC ACIDS
CARDIAC GLYCOSIDES
CARDIOTONICS
CARDIOVASCULAR AGENTS
CENTRAL NERVOUS SYSTEM
CHARGED PARTICLES
DRUGS
ELEMENTS
GLYCOSIDES
IONS
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LABELLED COMPOUNDS
LIGHT NUCLEI
MAMMALS
METALS
NERVOUS SYSTEM
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANS
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REACTION KINETICS
RODENTS
SODIUM ISOTOPES
SOMATIC CELLS
STROPHANTHINS
VERTEBRATES
YEARS LIVING RADIOISOTOPES
550201* - Biochemistry- Tracer Techniques