| Budget Amount *help |
¥11,300,000 (Direct Cost: ¥11,300,000)
Fiscal Year 2005: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2004: ¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 2003: ¥7,600,000 (Direct Cost: ¥7,600,000)
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| Research Abstract |
In single cardiomyocytes isolated from the adult rat, we investigated changes in intracellular oxygen concentration, mitochondrial oxidative metabolism, intracellular ATP concentration, and mitochondrial membrane potential using newly devised fluorescence imaging system. At physiological oxygen concentration (3%-5%),elevating oxygen flux to mitochondria by an uncoupler of oxidative phosphorylation promoted necrotic cell death. Because changes in the mitochondrial membrane potential in these cells were minimum, increases in the oxygen flux appeared to critically affect cell survival in hypoxia. Observed cell death was significantly accelerated after inhibition of creatine kinase (CK). In CK-inhibited cardiomyocytes with elevated oxygen flux, membrane potential was almost abolished in the cell core that is consistent with our previous findings regarding radial gradients of oxygen concentration within a single cardiomyocyte (anoxic cell core). Disruption of mitochondrial membrane potentia
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l in the anoxic core would turn the F_1F_0-ATP synthase (complex V) to an ATPase. If these happen, not only oxidative ATP production would be unable to proceed, but also massive consumption of ATP should break out in mitochondria in the anoxic core. This deficiency of ATP, albeit restricted in the cell core, quickly disturbs ATPase-dependent intracellular regulations of Ca^<2+>, and Ca^<2+> overload leading to cell death would finally commence. However, in the normal cardiomyocyte, the PCr-CK system may supply high energy phosphate from the cell surface (where oxygen is abundant and oxidative ATP production is not hampered) to the oxygen deficit cell core by diffusion. Thus, PCr originally produced in mitochondria near the cell surface would supplement ATP to the mitochondria in the anoxic cell core, so that mitochondrial membrane potential is maintained without electron transport in the respiratory chain. Functional disintegration of the mitochondria and following Ca^<2+> overload could be significantly retarded by this mechanism. Hence, the PCr-CK system may be an intrinsic mechanism that protects respiring cardiomyocytes against hypoxic death. Less
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