Effect of Glutamine on Glutamate Release from Hippocampal Slices Induced by High K+ or by Electrical Stimulation: Interaction with Different Ca2+ Concentrations

Publisher Website
Google Scholar
Abstract
To characterize the effect of glutamine on the release of glutamate, aspartate and GABA, rat hippocampal slices were superfused with different concentrations of glutamine or Ca2+. Amino acids released and retained were analyzed by HPLC [high performance liquid chromatography]. Glutamine (0.5 mmol/L) increased > 3-fold the release of glutamate evoked by 50 mmol/l K- in the presence of 2.6 mmol/l Ca2+ without a corresponding increase in glutamate content, while the release of aspartate was increased less and that of GABA not at all by glutamine. The evoked release of all 3 amino acids, including the enhanced release of glutamate in the presence of glutamine, was strongly dependent on Ca2+ concentrations between 0.1 and 2.6 mmol/l. The potentiation of glutamate release by glutamine reached a plateau at 0.25 mmol/l glutamine. Intermittent electrical field stimulation increased the release of only glutamate and this release was nearly doubled by glutamine. The increased release was Ca2+ dependent and tetrodotoxin (TTX) sensitive. Evidently, extracellular glutamine promotes primarily the formation of releasable glutamate and this enhancement is dependent on extracellular Ca2+.