Basic analysis for the role of Na+/Ca2+ exchanger on ischemic brain damage to establish new brain resusciataion method

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To investigate the mechanisms of ischemic neuronal cell death, we explored the planned experiments to focus on the relationship between the function of astrocytic Na+/Ca2+ exchanger and intracerebral Ca2+ dynamics, calcineurin/immunophilin cascade, and mitochondrial dysfunction based on Mitochondrial Permeability Transition(MPT) and also investigated the role of Na+/Ca2+ exchanger for the formation of ischemic neuronal cell death. We have used Na+/Ca2+ exchanger KO mouse(NCXKO) for our experiments.From our pathohistological analysis, NCXKO group did not show any protective effect in mice forebrain ischemia model. NCXKO mice hippocampal slice experiments showed the high intracellular Ca2+ level but not mitochondrial compared to wild group, however, Cyclosporin A also inhibited both the rise of intracellular and intramitochondrial Ca2+ as same as wild group. NCXKO group and wild group showed no significant difference in terms of mitochondrial swelling and calcium retension capacity(CRC) due to Ca2+ overlaod.Respiratory control ratio(RCR) in NCXKO mice showed high oxygen consumption at state 3. From our results, we could speculate the reason why we could not get neuroprotectio is that mice was not homozygous, so gene deletion was not enough to explore the neuroprotection. But from the results of hippocampal slice experiments, we considered that NCX is somehow deleted. Mitochondrial permeability transition was induced in both NCXKO and wild mice and these results suggested that NCX gene deletion does not affect the inhibition of mitochondrial dysfunction. We have speculated the reseason why oxygen consumption was high in NCXKO mice is that Ca2+ extrusion to extracellular space in NCXKO mice need long time compared to wild one, so mitochondria need to produce ATP consuming huge amount of oxygen. From our results, importance of Na+/Ca2+ exchanger was explored.