A glia-neuron alanine/ammonium shuttle is central to energy metabolism in bee retina

Coles, J. A., Martiel, J.-L. and Laskowska, K. (2008) A glia-neuron alanine/ammonium shuttle is central to energy metabolism in bee retina. Journal of Physiology, 586(8), pp. 2077-2091. (doi: 10.1113/jphysiol.2007.148734)

Abstract

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 inline image, 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 inline image. 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 inline image in normal superfusate. Lactate (l and d) and pyruvate (but not glucose) increased inline image 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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Coles, Dr Jonathan
• Authors: Coles, J. A., Martiel, J.-L., and Laskowska, K.
• College/School: College of Medical Veterinary and Life Sciences > School of Infection & Immunity
• Journal Name: Journal of Physiology
• Publisher: Wiley
• ISSN: 0022-3751
• ISSN (Online): 1469-7793