The uptake of L-glutamate by the retina.
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.
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D001345:Autoradiography; D004140:Dinitrophenols / Q000494:pharmacology; D005971:Glutamates / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism; D007461:Iodoacetates / Q000494:pharmacology; D007700:Kinetics; D009457:Neuroglia / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D012160:Retina / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D013696:Temperature; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D000596:Amino Acids; D004140:Dinitrophenols; D005971:Glutamates; D007461:Iodoacetates; D005973:Glutamine; D001224:Aspartic Acid; D005680:gamma-Aminobutyric Acid; D010042:Ouabain; D002731:4-Chloromercuribenzenesulfonate; D012964:Sodium