THE EFFECTS OF AGE AND PHYSICAL-ACTIVITY ON CARDIAC MITOCHONDRIAL-DNATEMPLATE AVAILABILITY

The purpose of this study was to examine the effects of aging and phys ical activity on heart mtDNA template availability, Young, mature and aged C57BL6 mice were used in this study with half of the animals havi ng access to exercise wheels, Cardiac DNA was isolated and the mitocho ndrial DNA content was assessed by slot blots with a specific mtDNA pr obe, Mitochondrial DNA template availability increased in mouse cardia c tissue with senescence. This was reflected in increases in mitochond rial DNA content per milligram of cardiac tissue and mitochondrial DNA relative to nuclear DNA ratios. Oxidative capacity, as determined by citrate synthase activity, was not significantly decreased with aging, Compromises to the energy transducing pathway due to aging responses in cardiac tissue may have led to higher replicative rates of mtDNA to induce more mitochondrial specific proteins. The mature mice responde d positively to the voluntary chronic physical activity displaying inc reased mitochondrial DNA to nuclear DNA ratios and elevated citrate sy nthase activities, Thus the increasing metabolic demand put on the mit ochondrial system was associated with elevated mtDNA template levels i n these animals, In contrast, the senescent animals' mtDNA template co ntent was unaffected by the physical activity, This lack of a relation ship in the senescent animals is most likely due to low running veloci ties and therefore relative workloads in this age group, but this sugg estion remains to be confirmed.