Calcium-mediated damage following hypoxia in cerebral cortex ex vivo studied by NMR spectroscopy. Evidence for direct involvement of voltage-gated Ca2+-channels
التفاصيل البيبلوغرافية
العنوان:
Calcium-mediated damage following hypoxia in cerebral cortex ex vivo studied by NMR spectroscopy. Evidence for direct involvement of voltage-gated Ca2+-channels
Calcium plays a prominent role in the neuronal degeneration which accompanies stroke and there has been much conjecture about the possible source of this Ca 2+ . The transmembrane Ca 2+ transporting processes are considered likely candidates for the ischemia-induced rise in intracellular Ca 2+ . In the present paper we have monitored metabolism in the cerebral cortex in vitro before, during and after aglycaemic hypoxia using 31 P and 1 H NMR spectroscopy. We used the recovery of cellular metabolites phosphocreatine, ATP, lactate, glutamate and N -acetyl aspartate determined by NMR as an indicator of cell damage caused by hypoxia. Phosphocreatine concentration recovered to only ∼58% of its control level following 15 min of aglycaemic hypoxia in the presence of 1.2 mM Ca 2+ . The ratios of phosphocreatine/ATP, lactate/ N -acetyl aspartate and glutamate/ N -acetyl aspartate did not differ at 1 h of recovery from the prehypoxia levels showing that the hypoxia resistant cells were metabolically viable. In the absence of external Ca 2+ , phosphocreatine recovery improved to ∼80%. Ten mM Mg 2+ or 25 μM diltiazem in the presence of 1.2 mM Ca 2+ improved recovery of phosphocreatine to ∼85%. Two other antagonists of L-type type voltage-gated Ca 2+ -channels, verapamil and nifedipine, did not protect the cerebral cortex from hypoxic damage. N- methyl- d -aspartate (100 μM) applied during hypoxia with 1.2 mM Ca 2+ did not augment the loss of phosphocreatine indicating that the cellular damage was not potentiated by the drug, even when 30 mM K + was present. The presence of N- methyl- d -aspartate did not weaken the protective effect of diltiazem. Blockade of N- methyl- d -aspartate or non -N- methyl- d -aspartate channels did not alleviate cellular damage caused by hypoxic insult. The present results suggest that the immediate, Ca 2+ -mediated neuronal damage in the cerebral cortex may be mediated by Ca 2+ influx through L-type voltage-gated Ca 2+ -channels.