Glutamate neurotoxicity in rat cerebellar granule cells involves cytochrome c release from mitochondria and mitochondrial shuttle impairment

To gain some insight into the mechanism by which glutamate neurotoxicity ta kes place in cerebellar granule cells, two steps of glucose oxidation were investigated: the electron flow via respiratory chain from certain substrat es to oxygen and the transfer of extramitochondrial reducing equivalents vi a the mitochondrial shuttles. However, cytochrome c release from intact mit ochondria was found to occur in glutamate-treated cells as detected photome trically in the supernatant of the cell homogenate suspension. As a result of cytochrome c release, an increase of the oxidation of externally added N ADH was found, probably occurring via the NADH-b(5) oxidoreductase of the o uter mitochondrial membrane. When the two mitochondrial shuttles glycerol 3 -phosphate/dihydroxyacetone phosphate and malate/oxaloacetate, devoted to o xidizing externally added NADH, were reconstructed, both were found to be i mpaired under glutamate neurotoxicity. Consistent early activation in two N ADH oxidizing mechanisms, i.e,, lactate production and plasma membrane NADH oxidoreductase activity, was found in glutamate-treated cells. In spite of this, the increase in the cell NADH fluorescence was found to be time-depe ndent, an index of the progressive damage of the cell.