The senescent heart has decreased systolic and diastolic functions, both of which could be related to alterations in cardiac sarcoplasmic reticulum (SR) calcium (Ca(2+)) handling. The purpose of this study was to determine if SR protein content and rates of Ca(2+) release and uptake and ATPase activity are lower in the senescent (34-36mo) Fisher 344×Brown-Norway F1 hybrid rat heart and if a long-term exercise training program could maintain SR function. Late middle aged (29mo) male rats underwent 5-7mo of treadmill training. Aging resulted in a decrease in SERCA activity and modest decrease in the rate of Ca(2+) uptake but no change in Ca(2+) release rate. SERCA2a content was not decreased with age but nitrotyrosine accumulation was increased and Ser16 phosphorylated phospholamban (PLN) was decreased. Ryanodine receptor content was not decreased with age but dihydropyridine receptor content was decreased in the senescent heart. Treadmill training had no significant effect on any of the SR properties or protein contents in the senescent rat heart. These results suggest that decreases in Ca(2+) uptake and SERCA activity in the senescent F344BN rat heart are due to increased SERCA2a damage from nitrotyrosine accumulation and inhibition by PLN and that exercise training initiated at late middle age is unable to prevent these age-related changes in cardiac SR function.