Akt phosphorylation and cell survival after hypoxia-induced cytochrome c release in superfused respiring neonatal rat cerebrocortical slices.

Abstract

Phosphorylation of Akt before hypoxia (30 min) and during reoxygenation (4 h) was evaluated in superperfused neonatal rat cerebrocortical slices (350 microm, P7, Sprague-Dawley). Cytosolic cytochrome c intensities in Western blots, which were increased at the end of hypoxia. were decreased during reoxygenation. Western blot intensities of phosphorylated Akt (phospho-Akt), nearly undetectable at the end of hypoxia, recovered quickly during reoxygenation, in a trend opposite that for cytochrome c. At 1.5 h and 4 h after hypoxia they became larger or the same as before hypoxia. Total Akt was unchanged by hypoxia and reoxygenation. Phosphocreatine (PCr) and nucleotide triphosphates (NTP) were measured in parallel 14.1 Tesla ex vivo 31P NMR superfused brain slice studies. PCr and alpha-NTP were nearly undetectable at the end of hypoxia. Although they recovered quickly after hypoxia, they were lower than before hypoxia. Reductions in phospho-Akt during hypoxia were consistent with the general unavailability of basic high energy phosphates. Preferential phosphorylation of Akt after hypoxia suggested that substantial reductions in intracellular energy, as indicated by PCr and NTP, might be tolerated by processes important for generating phospho-Akt. Additionally, the post-hypoxia increase in phospho-Akt might have contributed to concomitant reductions in cytosolic cytochrome c.