Differential Effects of Exercise on Interfibrillar and Subsarcolemmal Skeletal Muscle Mitochondria

High inborn running capacity (HCR) is a strong predictor for all-cause morbidity and is considered to affect outcome in cardiac surgery. Mitochondria play a key role in mediating exercise effects. We demonstrated that genetic predisposition influences the mitochondrial response to exercise training as rats with HCR responded to exercise training, while rats with low inborn running capacity did not. Since there are two types of mitochondria (subsarcolemmal, SSM and interfibrillar, IFM), we assessed the effect of exercise training on the properties of these two mitochondrial subpopulations in skeletal muscle of HCR. It is the common notion that IFM generate ATP for contractile function and SSM for cell and membrane maintenance.

IFM and SSM were isolated by differential centrifugation from M. gastrocnemius of exercise trained or sedentary HCR. Citrate synthase activity and protein content were determined photometrically, and respiratory capacity was measured using a Clark-type electrode.

Exercise training resulted in increased body weight, cardiac hypertrophy, and increased muscle weight. Exercise increased citrate synthase activity. Respiratory capacity of SSM was higher than of IFM in sedentary animals with substrates for complex I (173 ± 29 vs. 86 ± 18 all nAtomO/min/mgprot), complex II (260 ± 37 vs. 202 ± 19), complex III (431 ± 94 vs. 222 ± 34), and complex IV (574 ± 63 vs. 489 ± 42). ADP/O ratios were not different between SSM and IFM. Exercise training led to an increase in respiratory capacity in IFM (CI 86 ± 18 vs. 112 ± 17; CII 202 ± 19 vs. 278 ± 42; CIII 222 ± 34 vs. 422 ± 52; CIV 489 ± 42 vs. 620 ±85 nAtoms O/min/mgprot) but not in SSM reducing the difference between both populations ADP/O ratio was not affected by exercise.

Exercise training in rats improves respiratory capacity only in interfibrillar mitochondria of skeletal muscle. These data are consistent with the notion that IFM produce ATP mainly for contractile function.

No conflict of interest has been declared by the author(s).