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Title: 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+more » 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.« less
Authors:
; ;
Publication Date:
OSTI Identifier:
6258041
Resource Type:
Journal Article
Resource Relation:
Journal Name: J. Neurosci.; (United States); Journal Volume: 9:4
Research Org:
Albany Medical College, Albany, NY (USA)
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; 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; RADIOISOTOPES; REACTION KINETICS; RODENTS; SODIUM ISOTOPES; SOMATIC CELLS; STROPHANTHINS; VERTEBRATES; YEARS LIVING RADIOISOTOPES 550201* -- Biochemistry-- Tracer Techniques