Calcium uptake in skeletal muscle mitochondria

Summary

In order to ascertain the effects of long-term exercise training and long-term exhaustive exercise on mitochondrial ⁴⁵Ca²⁺ uptake and related variables in rat skeletal muscle, female rats were randomly divided into three groups: sedentary-rested (SR), trained-rested (TR), and trained-exhausted (TE). The trained groups were exercised five times per week on a treadmill for 22 weeks. At the conclusion of the training period, the TE group was exercised to exhaustion following their daily 1 h run. The ⁴⁵Ca²⁺ uptake and endogenous mitochondrial Ca²⁺ content of skeletal muscle followed stepwise increases of approximately 25% and 50%, respectively, across the groups, suggesting that long-term exercise induces the mitochondria to play an important role as a Ca²⁺ ion buffer. A 75–83% reduction in ⁴⁵Ca²⁺ binding in the TE group suggests a selective loss and partial saturation of membrane phospholipids with exhaustive exercise. The TE group had a two-fold greater content of mitochondrial Mg²⁺ than did the rested groups. It is speculated that the mitochondria accumulate Mg²⁺ during acute exercise to maintain the functional integrity of the membrane, thus offsetting the deleterious effects of excessive Ca²⁺ uptake.