Inhibition by anion channel blockers of ischemia-evoked release of excitotoxic and other amino acids from rat cerebral cortex

Abstract

Neuronal and glial cell swelling occurs rapidly in ischemia as part of the cytotoxic response. Astrocytic swelling is known to result in large extracellular increases in certain amino acids, including glutamate, aspartate and taurine, as part of the regulatory volume decrease (RVD) response inherent to these and other cells. RVD in astrocytic cultures is inhibited by anion channel blockers. In this study, we compared the effects of three anion channel blockers on the ischemia/reperfusion-evoked release of amino acids from the in vivo rat cerebral cortex. Twenty minutes of four vessel cerebral ischemia caused significant increases in cortical superfusate levels of aspartate, glutamate, GABA, taurine and phosphoethanolamine. During reperfusion there were delayed increases the level of glycine, alanine and serine. Glutamine levels were not affected. Cl − channel blockers, 4-acetamido-4′-isothiocyanostrilbene-2,2′-disulfonic acid (SITS, 2 mM), 5-nitro-2-(3-phenyl-propylamino)benzoic acid (NPPB, 350 μM) and dipyridamole (200 μM) depressed basal releases of glutamate and taurine and the ischemia/reperfusion-evoked releases of aspartate, glutamate, taurine and phosphoethanolamine. The results suggest that diffusion of amino acids through an anion channel may be partially responsible for the elevated extracellular levels of excitotoxic and other amino acids that occur during cerebral ischemia/reperfusion.