Effect of physical conditioning on cardiac mitochondrial function

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Abstract
Mitochondria isolated from hearts of sedentary rats (SH) were compared with mitochondria isolated from hearts of physically conditioned rats (CH) trained by swimming. Measurement of mitochondrial respiratory activity indicated no change in ADP:O ratio and respiratory control index, but the state 3 O2 consumption per mg mitochondrial protein was 15% less in CH than SH. The measurement of mitochondrial Ca uptake, energy-independent and respiratory-supported Ca uptake in the absence of ATP or ADP, showed no differences between the groups. Ca uptake per mg mitochondrial protein was depressed 25% in the CH when respiratory substrates (glutamate and malate or succinate) and 1-10 mM Mg-ATP or 3-10 mM Mg-ADP were present. No differences were observed between the groups in the total mitochondrial recovery, mitochondrial cytochrome oxidase activity, mitochondrial ATPase activity and mitochondrial Ca content when the results were expressed per mg mitochondria. Estimation of mitochondrial content per g wet heart wt indicated a 52% increase in mitochondrial protein in CH compared to SH. Despite diminished oxidative and Ca uptake activity (in the presence of ATP) per mg mitochondria, the absolute oxidative phosphorylation and Ca uptake per g tissue apparently was not decreased in conditioned hearts and might even be increased. These changes in the mitochondrial functions probably reflect a long-term adaptation of rat heart to physical training.