Elsevier

Brain Research

Volume 111, Issue 1, 23 July 1976, Pages 79-93
Brain Research

The uptake ofl-glutamate by the retina

https://doi.org/10.1016/0006-8993(76)91050-7Get rights and content

Abstract

The accumulation ofl-[14C]glutamate by the isolated rat retina has been studied. When retinae were incubated at 37 °C in a medium containingl-[14C]glutamate, tissue/medium ratios of about 40:1 were achieved after 60 min. The labelledl-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 forl-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 (apparentKm= 21 μM,Vmax= 35nmoles/min/g tissue) and a ‘low’ affinity process (Km = 630 μM,Vmax= 881nmoles/min/g tissue). The ‘high’ affinity and ‘low’ affinity uptake processes forl-glutamate appeared to have identical properties in the retina.

The uptake ofl-glutamate was not specific and was inhibited by other acidic amino acids includingd-glutamate but not by neutral or basic or amino acids.

The retinal uptake ofl-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 ofl-[14C]glutamate from the tissue was not increased by the addition of non-radioactivel-glutamate to the incubation medium.

Autoradiographic studies indicated that the sites for glutamate uptake are largely in the neuroglial Mu¨ller cells.

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