Glutamine-mediated protection from neuronal cell death depends on mitochondrial activity

The specific aim of this study was to elucidate the role of mitochondria in a neuronal death caused by different metabolic effectors and possible role of intracellular calcium ions (Ca²⁺]_i) and glutamine in mitochondria- and non-mitochondria-mediated cell death. Inhibition of mitochondrial complex I by rotenone was found to cause intensive death of cultured cerebellar granule neurons (CGNs) that was preceded by an increase in intracellular calcium concentration (Ca²⁺]_i). The neuronal death induced by rotenone was significantly potentiated by glutamine. In addition, inhibition of Na/K-ATPase by ouabain also caused Ca²⁺]_i increase, but it induced neuronal cell death only in the absence of glucose. Treatment with glutamine prevented the toxic effect of ouabain and decreased Ca²⁺]_i. Blockade of ionotropic glutamate receptors prevented neuronal death and significantly decreased Ca²⁺]_i, demonstrating that toxicity of rotenone and ouabain was at least partially mediated by activation of these receptors. Activation of glutamate receptors by NMDA increased Ca²⁺]_i and decreased mitochondrial membrane potential leading to markedly decreased neuronal survival under glucose deprivation. Glutamine treatment under these conditions prevented cell death and significantly decreased the disturbances of Ca²⁺]_i and changes in mitochondrial membrane potential caused by NMDA during hypoglycemia. Our results indicate that glutamine stimulates glutamate-dependent neuronal damage when mitochondrial respiration is impaired. However, when mitochondria are functionally active, glutamine can be used by mitochondria as an alternative substrate to maintain cellular energy levels and promote cell survival.