Activation of voltage-sensitive sodium channels during oxygen deprivation leads to apoptotic neuronal death

Sodium (Na+) entry into neurons during hypoxia is known to be associated with cell death. However, it is not clear whether Na+ entry causes cell death and by what mechanisms this increased Na+ entry induces death. In this study we used cultures of rat neocortical neurons to show that an increase in intracellular sodium (Na+) through voltage-sensitive sodium channels (VSSCs), during hypoxia contributes to apoptosis. Hypoxia increased Na-i(+) and induced neuronal apoptosis, as assessed by electron microscopy, annexin V staining, and terminal UDP nick end labeling staining. Reducing Na+ entry with the VSSC blocker, tetrodotoxin (TTX), attenuated apoptotic neuronal death via a reduction in caspase-3 activation. Since the attenuation of apoptosis by TTX during hypoxia suggested that the activation of VSSCs and Na+ entry are crucial events in hypoxia-induced cell death, we also determined whether the activation of VSSCs per se could lead to apoptosis under resting conditions. Increasing Na+ entry with the VSSC activator veratridine also induced neuronal apoptosis and caspase-3 activation. These data indicate that a) Na+ entry via VSSCs during hypoxia leads to apoptotic cell death which is mediated, in part, by caspase-3 and b) activation of VSSCs during oxygen deprivation is a major event by which hypoxia induces cell death. (C) 2004 Published by Elsevier Ltd on behalf of IBRO.