title: Effect of glucose deprivation on rat glutamine synthetase in cultured astrocytes.
abstract: Glutamine synthetase was purified from the cerebral cortex of adult rats and characterized. Polyclonal rabbit antibodies were raised against the enzyme, purified and their specific anti-(glutamine synthetase) activity determined. A primary astroglial culture was prepared from newborn Sprague-Dawley rats. Astrocytes at different ages of development were incubated in the presence and absence of glucose. In glucose-deprived conditions the specific activity of glutamine synthetase decreased. This decrease was more pronounced in 8-day-old than in 21-day-old cultures. Kinetic analysis demonstrated that the reduction in activity was mainly related to a decrease in Vmax. By immunoprecipitation, it was shown that the number of enzyme molecules in astrocytes was decreased in glucose-deprived conditions. On addition of glucose, a total recovery of glutamine synthetase was obtained after 36 h in 8-day-old culture. Rates of degradation and synthesis were investigated. When compared with an incubation in the presence of glucose, glucose deprivation increased enzyme turnover, as estimated from the first-order disappearance of radioactivity from glutamine synthetase. Synthesis rate was estimated from the incorporation of [35S]methionine during a 2 h incubation period and was decreased in glucose-deprived conditions. Trichloroacetate-precipitable proteins changed only slightly in the experimental conditions, and total protein did not vary significantly during the experimental period. A mathematical model is presented which attempts to integrate degradation and synthesis in our experimental model.
authors.affiliation: Laboratory of Pharmacology and Physiology, Facultés Universitaires, Namur, Belgium.
authors.forename: F
authors.initials: F
authors.lastname: Rosier
authors.forename: D
authors.initials: D
authors.lastname: Lambert
authors.forename: M
authors.initials: M
authors.lastname: Mertens-Strijthagen
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D000906:Antibodies; D001253:Astrocytes / Q000187:drug effects* / Q000201:enzymology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000201:enzymology; D005947:Glucose / Q000494:pharmacology*; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D011817:Rabbits; D051381:Rats
chemical_list: D000906:Antibodies; D005974:Glutamate-Ammonia Ligase; D005947:Glucose