Responses to reversible anoxia of intracellular free and bound Ca2+ in ratcortical slices

Severe anoxia induces destabilisation of intracellular calcium homeostasis in neurones. The mechanism of this effect, and particularly the interrelati onship between changes in intracellular concentration of free Ca2+ ions and the content of the intracellular Ca2+ stares, during and after anoxia, is not clear. We used a superfusion system of rat olfactory cortical slices fo r the fluorimetric estimation of changes in the intracellular concentration of free Ca2+ ions and in the level of bound Ca2+, utilising the fluorescen t indicators Fura-2 and chlortetracycline, respectively. It was found that 10-min normoglycaemic anoxia results in simultaneous decrease in bound and increase in free Ca2+ levels, whereas during 60-min reoxygenation, we detec ted an increase in both indices. The NMDA receptor antagonists MK-801 and A PV attenuated changes in free Ca2+ level during anoxia and reoxygenation an d intensified anoxia-evoked decrease in bound Ca2+ content, whereas a late post-anoxic increase in bound Ca2+ was abolished. These data suggest that t he influx of extracellular Ca2+ to neurones via NMDA receptors, plays a cri tical role in the rise of intracellular free Ca2+ concentration during and after anoxia. Biphasic changes in bound Ca2+ content during anoxia and reox ygenation may reflect an anoxia-induced release of Ca2+ from intracellular stores, followed later by a neuronal calcium overload and refilling of intr acellular Ca2+ binding sites. (C) 2000 Elsevier Science Ireland Ltd. All ri ghts reserved.