Mechanisms of glutamate release elicited in rat cerebrocortical nerve endings by 'pathologically' elevated extraterminal K+ concentrations |
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Authors: | Raiteri Luca Zappettini Simona Milanese Marco Fedele Ernesto Raiteri Maurizio Bonanno Giambattista |
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Institution: | Department of Experimental Medicine, Pharmacology and Toxicology Section, University of Genoa, Genoa, Italy. |
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Abstract: | Extracellular K+] can increase during some pathological conditions, resulting into excessive glutamate release through multiple mechanisms. We here investigate the overflow of 3H]D-aspartate (3H] D-ASP) and of endogenous glutamate elicited by increasing K+] from purified rat cerebrocortical synaptosomes. Depolarization with K+] 15 mmol/L were prevented by the glutamate transporter inhibitors DL-threo-beta-benzyloxyaspartate (DL-TBOA) and dihydrokainate. Differently, the overflows of endogenous glutamate provoked by K+] > 15 mmol/L were insensitive to both inhibitors; the external Ca2+-independent glutamate overflow caused by 50 mmol/L KCl was prevented by bafilomycin, by chelating intraterminal Ca2+, by blocking the mitochondrial Na+/Ca2+ exchanger and, for a small portion, by blocking anion channels. In contrast to purified synaptosomes, the 50 mmol/L K+-evoked release of endogenous glutamate or 3H]D-ASP was inhibited by DL-TBOA in crude synaptosomes; moreover, it was external Ca2+-insensitive and blocked by DL-TBOA in purified gliosomes, suggesting that carrier-mediated release of endogenous glutamate provoked by excessive K+] in CNS tissues largely originates from glia. |
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Keywords: | Ca2+ pools carrier-mediated release excitatory amino acid transporters exocytosis glutamate release pathological [K+] |
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