Alterations in mitochondrial RNA expression after renal ischemia.

Ischemia and reperfusion damage mitochondrial structure and impair respiratory function. In this study, 45 min of renal ischemia followed by varying periods of reflow profoundly depressed the activity of several respiratory complexes in mitochondria isolated from rat kidneys. The respiratory complexes are composed of subunits encoded by both the nuclear and mitochondrial genomes. To determine the role of mitochondrial gene expression in recovery of respiratory function, expression of mitochondrial RNA was examined during reperfusion. Both mature and incompletely processed cytochrome b mRNA levels were depressed after 45 min of ischemia and 15 min of reflow; levels rebounded to above normal after 2 h of reflow and then declined over the next 22 h. Another mitochondrial RNA showed a similar pattern; in contrast, the levels of a nuclear-encoded subunit mRNA for a respiratory enzyme and of 28S rRNA were unchanged. These data demonstrate that renal ischemia followed by reperfusion alters mitochondrial RNA expression. We speculate that mitochondrial RNA turnover is increased in response to continuing injury and that recovery is accompanied by enhanced RNA synthesis.