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This Article Full Text Full Text (PDF) All Versions of this Article: 586/8/2077    most recent jphysiol.2007.148734v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Coles, J. A. Articles by Laskowska, K. PubMed PubMed Citation Articles by Coles, J. A. Articles by Laskowska, K. Related Collections Neuroscience

¹ INSERM U836, Grenoble, France
² Université Joseph Fourier,Grenoble Institut des Neurosciences, Grenoble, France
³ Laboratoire TIMC UMR CNRS 5525, équipe TIMB, Institut d'Ingénierie de l'Information de Santé, Faculté de Médecine, Grenoble, France

It has been proposed that glial cells may supply carbon fuel to neurons and also that there are fluxes of ammonium from neurons to glia. We have investigated both these proposals in Apis retinal slices, in which virtually all the mitochondria are in the photoreceptor neurons. Normally the superfusate contained no substrate of energy metabolism; addition of glucose or alanine did not increase oxygen consumption , confirming that the neurons received adequate substrate from glycogen in the glia. 1,4-Dideoxy-1,4-imino-D-arabinitol (DAB, 100 µM), an inhibitor of glycogen phosphorylase, progressively decreased . This decrease was reversed by alanine but not glucose. Ammonium-sensitive microelectrodes did not detect significant extracellular [NH₄⁺] ([NH₄⁺]_e) in slices superfused with normal superfusate. Removal of Cl^–, necessary for cotransport of NH₄⁺ into the glia, increased [NH₄⁺]_e so that at the end of 2 min photostimulation mean [NH₄⁺]_e was 0.442 mM (S.E.M. = 0.082 mM, n = 16). In 0 Cl^–, [NH₄⁺]_e was reduced by 2-(methylamino)isobutyrate (MeAIB) an inhibitor of alanine transport. MeAIB also blocked oxidation of alanine in the presence of DAB, but did not decrease in normal superfusate. Lactate (L and D) and pyruvate (but not glucose) increased in DAB and decreased [NH₄⁺]_e in 0 Cl^–. These results strengthen the evidence that in superfused retinal slices, glucose is metabolized exclusively in the glia, which supply alanine to the neurons, and that ammonium returns to the glia. They also show that another fuel (perhaps lactate) can be supplied by the glia to the neurons.

(Received 23 November 2007; accepted after revision 12 February 2008; first published online 14 February 2008)
Corresponding author J. A. Coles: GIN, Equipe 5, Université Joseph Fourier, Site Santé de la Merci, F-38706 La Tronche cedex, France. Email: jonathan.coles{at}ujf-grenoble.fr