title: Ammonium and glutamate released by neurons are signals regulating the nutritive function of a glial cell.
abstract: Glial cells transform glucose to a fuel substrate taken up and used by neurons. In the honeybee retina, photoreceptor neurons consume both alanine supplied by glial cells and exogenous proline. Ammonium (NH4+) and glutamate, produced and released in a stimulus-dependent manner by photoreceptor neurons, contribute to the biosynthesis of alanine in glia. Here we report that NH4+ and glutamate are transported into glia and that a transient rise in the intraglial concentration of NH4+ or of glutamate causes a net increase in the level of reduced nicotinamide adenine dinucleotides [NAD(P)H]. Biochemical measurements indicate that this is attributable to activation of glycolysis in glial cells by the direct action of NH4+ and glutamate on at least two enzymatic reactions: those catalyzed by phosphofructokinase (PFK; ATP:D-fructose-6-phosphotransferase, EC2.7.1.11) and glutamate dehydrogenase (GDH; L-glutamate:NAD oxidoreductase, deaminating; EC1.4.1.3). This activation leads to an increase in the production and release of alanine by glia. This signaling, which depends on the rate of conversion of NH4+ and glutamate to alanine and alpha-ketoglutarate, respectively, in the glial cells, raises the novel possibility of a tight regulation of the nutritive function of glia.
authors.affiliation: Experimental Ophthalmology Laboratory, University of Geneva Medical School, 1211 Geneva 4, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Tsacopoulos
authors.forename: C L
authors.initials: CL
authors.lastname: Poitry-Yamate
authors.forename: S
authors.initials: S
authors.lastname: Poitry
mesh_terms: D000818:Animals; D001516:Bees; D002450:Cell Communication; D018698:Glutamic Acid / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D008959:Models, Neurological; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009457:Neuroglia / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D012160:Retina / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D000644:Quaternary Ammonium Compounds; D009243:NAD; D018698:Glutamic Acid; D009249:NADP