title: Glutamine as an energy substrate in cultured neurons during glucose deprivation.
abstract: During glucose deprivation an increase in aspartate formation from glutamine has been observed in different brain preparations, including synaptosomes and cultured astrocytes. To what extent this reaction, which provides a substantial amount of energy, occurs in different types of neurons is unknown. The present study shows that (14)CO(2) formation from [U-(14)C]glutamine in cerebellar granule neurons, a glutamatergic preparation, increased by 60% during glucose deprivation, indicating enhanced aspartate formation or increased complete oxidative degradation of glutamine. In primary cultures of cerebrocortical interneurons, a GABAergic preparation, the rate of (14)CO(2) production from [U-(14) C] glutamine was four times lower and not stimulated by glucose deprivation. During incubation with glutamine (0.8 mM) as the only metabolic substrate, cerebellar granule cells maintained an oxygen consumption rate of 12 nmol/min/mg protein, corresponding to an aspartate formation of 8 nmol/min/mg protein (three oxidations occur between glutamine and aspartate) or to a total oxidative degradation of 3 nmol/min/mg protein. During glucose deprivation, the rate of aspartate formation increased, and during a 20-min incubation in phosphate-buffered saline it amounted to 3.3 nmol/min/mg protein at 0.2 mM glutamine, which might have been more if measured at 0.8 mM glutamine. These values are consistent with the rate of glutamine utilization calculated based on oxygen consumption and leaves open the possibility that some glutamine is completely degraded oxidatively, as has been shown by other authors based on pyruvate recycling and labeling of lactate from aspartate in cerebellar granule neurons.
authors.affiliation: Department of Clinical Pharmacology, China Medical University, Shenyang, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Peng
authors.forename: Li
authors.initials: L
authors.lastname: Gu
authors.forename: Hongliang
authors.initials: H
authors.lastname: Zhang
authors.forename: Xueshi
authors.initials: X
authors.lastname: Huang
authors.forename: Elna
authors.initials: E
authors.lastname: Hertz
authors.forename: Leif
authors.initials: L
authors.lastname: Hertz
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004734:Energy Metabolism / Q000502:physiology*; D005947:Glucose / Q000172:deficiency*; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism*; D051379:Mice; D009474:Neurons / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology
chemical_list: D005973:Glutamine; D001224:Aspartic Acid; D018698:Glutamic Acid; D005947:Glucose