Skeletal muscle aging in F344BNF1-hybrid rats:: I.: Mitochondrial dysfunction contributes to the age-associated reduction in VO2max

Although mitochondrial DNA damage accumulates in aging skeletal muscles, how this relates to the decline in muscle mass-specific skeletal muscle aerobic function is unknown. We used a pump-perfused rat hind-limb model to examine maximal aerobic performance (VO2max) in young adult (YA; 8-9-month-old), late middle aged (LMA; 28-30-month-old) and senescent (SEN; 36-month-old) Fischer 344 X Brown Norway F1-hybrid rats at matched rates of convective 02 delivery QO(2). Despite similar muscle QO(2) during a 4-minute contraction bout, muscle mass-specific VO2 was reduced in LMA (15%) and SEN (52%) versus YA. In plantaris muscle homogenates, nested polymerase chain reaction revealed an increased frequency of mitochondrial DNA deletions in the older animals. A greater reduction in the flux through electron transport chain complexes I-III than citrate synthase activity in the older animals suggests mitochondrial dysfunction consequent to mitochondrial DNA damage with aging. These results support the hypothesis that a reduced oxidative capacity, due in part to age-related mitochondrial dysfunction, contributes to the decline in aerobic performance in aging skeletal muscles.