PEROXYNITRITE CAUSES ASPARTATE RELEASE FROM DISSOCIATED RAT CEREBELLAR GRANULE NEURONS

Peroxynitrite (ONOO-) is a powerful oxidant which is formed from the r eaction between nitric oxide (NO) and superoxide anion. It has therefo re been proposed to mediate the toxic actions caused by NO. Since ONOO - may be formed in the central nervous system (CNS) in pathological co nditions such as brain ischaemia, we decided to investigate whether th is molecule induces the release of the endogenous excitatory amino aci ds glutamate and aspartate from neurones. We selected as biological mo del acutely dissociated rat cerebellar granule neurones in suspension to allow a direct interaction between ONOO- and target cells. Peroxyni trite caused a concentration-dependent release of aspartate but not of glutamate from dissociated cerebellar granule neurones. Peroxynitrite induced aspartate release was inhibited by dithiothreitol, tetrodotoxi n, and in Nat-deprived solutions and not affected by EGTA or pre-incub ation with the cytosolic Ca2+ chelator BAPTA/ AM. Peroxynitrite also i nduced an increase in intracellular Ca2+ concentration which was not a ffected in the presence of EGTA. These data show that ONOO- causes rel ease of aspartate from cerebellar granule neurones and that this effec t might arise from an alteration of Nac membrane permeability leading subsequently to reversal of a Na+-dependent plasma membrane transporte r of this excitatory amino acid. In addition, ONOO- alters Ca2+ homeos tasis likely due to Na+ overload. Taken together, these findings may h elp and elucidate some of the intimate mechanisms of NO-induced neuron al damage in pathological circumstances.