The uptake of L-glutamate by the retina

Brain Res. 1976 Jul 23;111(1):79-93. doi: 10.1016/0006-8993(76)91050-7.

Abstract

The accumulation of L[14C]glutamate by the isolated rat retina has been studied. When retinae were incubated at 37 degrees C in a medium containing L-[14C]glutamate, tissue/medium ratios of about 40:1 were achieved after 60 min. The labelled L-glutamate was rapidly metabolised and after 10 min about 50% of the radioactivity in the tissue amino acids was present as glutamine, aspartate, and 4-aminobutyrate (GABA). The process responsible for L-glutamate uptake showed many of the properties of an active uptake system: it was temperature sensitive, sodium dependent, inhibited by metabolic inhibitors and showed saturation kinetics. The saturable uptake process could be resolved into two components; a 'high' affinity process (apparent Km = 21 muM, Vmax = 35 nmoles/min/g tissue) and a 'low' affinity process (Km = 630 muM, Vmax = 881 nmoles/min/g tissue). The 'high' affinity and 'low' affinity uptake processes for L-glutamate appeared to have identical properties in the retina. The uptake of L-glutamate was not specific and was inhibited by other acidic amino acids including D-glutamate but not by neutral or basic amino acids. The retinal uptake of L-glutamate is not likely to be due to a homoexchange phenomenon because the retina was capable of achieving a large net uptake of glutamate and the efflux of L-[14C]glutamate from the tissue was not increased by the addition of non-radioactive L-glutamate to the incubation medium. Autoradiographic studies indicated that the sites for glutamate uptake are largely in the neuroglial Muller cells.

MeSH terms

  • 4-Chloromercuribenzenesulfonate / pharmacology
  • Amino Acids / pharmacology
  • Animals
  • Aspartic Acid / metabolism
  • Autoradiography
  • Dinitrophenols / pharmacology
  • Glutamates / metabolism*
  • Glutamine / metabolism
  • Iodoacetates / pharmacology
  • Kinetics
  • Neuroglia / metabolism
  • Ouabain / pharmacology
  • Rats
  • Retina / drug effects
  • Retina / metabolism*
  • Sodium / pharmacology
  • Temperature
  • gamma-Aminobutyric Acid / metabolism

Substances

  • Amino Acids
  • Dinitrophenols
  • Glutamates
  • Iodoacetates
  • Glutamine
  • Aspartic Acid
  • gamma-Aminobutyric Acid
  • Ouabain
  • 4-Chloromercuribenzenesulfonate
  • Sodium