MITOCHONDRIAL SITES OF HYDROGEN-PEROXIDE PRODUCTION IN REPERFUSED RAT-KIDNEY CORTEX

Electron transport and production of O-2(-)/H2O2 by the NADH dehydroge nase flavin-semiquinone (FMNH.) and ubisemiquinone (UQH(.)) were studi ed in a model of in vivo ischemia-reperfusion in rat kidney. H2O2 prod uction rates were assessed in isolated mitochondria using either succi nate, with and without antimycin, or malate-glutamate, with and withou t rotenone. Respiratory activities of isolated mitochondria and activi ty of NADH- and succinate-cytochrome c reductase and of NADH- and succ inate-dehydrogenase in submitochondrial particles were measured to eva luate the electron flux throughout respiratory carriers. The mitochond rial H2O2 production rate was approximately 1.5- and 4-times increased in ischemic and ischemic-reperfused kidneys, respectively. Ischemia c aused a marked decrease in the electron transport throughout the NADH- UQ segment with no significant changes either in the NADH dehydrogenas e activity or in the electron flux trough the succinate-cytochrome oxi dase segment. Reperfusion did not further affect the NADH-ubiquinone s egment but markedly inhibited the succinate-supported oxygen consumpti on, succinate-cytochrome c reductase and succinate dehydrogenase activ ity. Our results show a redistribution of the electron flux with an in creased rate of superoxide anion/hydrogen peroxide production at NADH dehydrogenase in mitochondria subjected to ischemia only. After 10 min reperfusion an impairment of the electron flow at succinate-cytochrom e c segment is established and hydrogen peroxide production by UQH(.) increases up to maximal values becoming the major source of superoxide anion/hydrogen peroxide.