Reduced mitochondrial DNA transcription in senescent rat heart

We studied the effect of senescence on mitochondrial DNA (mtDNA) transcript ion with an in organello system using intact isolated rat heart mitochondri a. A comparison of the electrophoretic patterns of mtDNA transcription prod ucts in young, adult and senescent rats showed an age-related reduction in newly-synthesized mitochondrial RNAs that reflects a decrease in the synthe sis rate. These results correlate with the enzyme activities of the oxidati ve phosphorylation complexes I and IV, that are partially encoded by the mi tochondrial genome. In addition, an age-related increase in the protein car bonyl content of the mitochondrial membranes was observed in senescent mito chondria suggesting an accumulation of mitochondrial oxidative damage. This reduction in the mtDNA transcriptional rate in the heart of senescent anim als suggests that this could be one of the molecular bases underlying senes cence of the myocardium. (C) 1998 Academic Press.