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Naϩ /Ca 2ϩ exchanger 3 (NCX3), one of the three isoforms of the NCX family, is highly expressed in the brain and is involved in the maintenance of intracellular Na ϩ and Ca 2ϩ homeostasis. Interestingly, whereas the function of NCX3 under physiological conditions has been determined, its role under anoxia is still unknown. To assess NCX3 role in cerebral ischemia, we exposed ncx3Ϫ/Ϫ mice to transient middle cerebral artery occlusion followed by reperfusion. In addition, to evaluate the effect of ncx3 ablation on neuronal survival, organotypic hippocampal cultures and primary cortical neurons from ncx3Ϫ/Ϫ mice were subjected to oxygen glucose deprivation (OGD) plus reoxygenation. Here we report that ncx3 gene suppression leads to a worsening of brain damage after focal ischemia and to a massive neuronal death in all the hippocampal fields of organotypic cultures as well as in cortical neurons from ncx3Ϫ/Ϫ mice exposed to OGD plus reoxygenation. In addition, in ncx3Ϫ/Ϫ cortical neurons exposed to hypoxia, NCX currents, recorded in the reverse mode of operation, were significantly lower than those detected in ncx3ϩ/ϩ. From these results, NCX3 protein emerges as a new molecular target that may have a potential therapeutic value in modulating cerebral ischemia.

1. In isolated pancreatic islets, pyruvate causes a shift to the left of the sigmoidal curve relating the rate of insulin release to the ambient glucose concentration. The magnitude of this effect is related to the concentration of pyruvate (5--90 mM) and, at a 30 mM concentration, is equivalent to that evoked by 2 mM-glucose. Pyruvate also enhances insulin release in the presence of fructose, leucine and 4-methyl-2-oxopentanoate. 2. In the presence of glucose 8 mM), the secretory response to pyruvate is an immediate process, displaying a biphasic pattern. 3. The insulinotropic action of pyruvate coincides with an inhibition of 45Ca efflux and a stimulation of 45Ca net uptake. The relationship between 45Ca uptake and insulin release displays its usual pattern in the presence of pyruvate. 4. Exogenous pyruvate rapidly accumulates in the islets in amounts close to those derived from the metabolism of glucose. The oxidation of [2-14C]pyruvate represents 64% of the rate of [1-14C]pyruvate decarboxylation and, at a 30 mM concentration, is comparable with that of 8 mM-[U-14C]glucose. 5. When corrected for the conversion of pyruvate into lactate, the oxidation of 30 mM-pyruvate corresponds to a net generation of about 314 pmol of reducing equivalents/120 min per islet. 6. Pyruvate does not affect the rate of glycolysis, but inhibits the oxidation of glucose. Glucose does not affect pyruvate oxidation. 7. Pyruvate (30 mM) does not affect the concentration of ATP, ADP and AMP in the islet cells. 8. Pyruvate (30 mM) increases the concentration of reduced nicotinamide nucleotides in the presence but not in the absence of glucose. A close correlation is seen between the concentration of reduced nicotinamide nucleotides and the net uptake of 45Ca. Menadione inhibits the effect of pyruvate on insulin release, without altering its rate of oxidation. 9. Pyruvate, like glucose, modestly stimulates lipogenesis. 10. Pyruvate, in contrast with glucose, markedly inhibits the oxidation of endogenous nutrients. The latter effect accounts for the apparent discrepancy between the rate of pyruvate oxidation and the magnitude of its insulinotropic action. 11. Dichloroacetate fails to affect glucose oxidation and glucose-stimulated insulin release. 12. It is concluded that the effect of pyruvate to stimulate insulin release depends on its ability to increase the concentration of reduced nicotinamide nucleotides in the islet cells.