Effect of body temperature during exercise on skeletal muscle cytochrome c oxidase content

This study determined the role of body temperature during exercise on cytochrome-c oxidase (CytOx) activity, a marker of mitochondrial content, and mitochondrial heat shock protein 70 (mtHSP70), which is required for import of nuclear-coded preproteins. Male, 10-wk-old, Sprague-Dawley rats exercised identically for 9 wk in ambient temperatures of 23degreesC (n = 10), 8degreesC with wetted fur (n = 8), and 4degreesC with wetted fur and fan (n = 7). These conditions maintained exercising core temperature (T-c) at 40.4, 39.2, or 38.0degreesC (resting temperature), respectively. During weeks 3-9, exercisers ran 5 days/wk up a 6% grade at 20 m/min for 60 min. Animals were housed at 23degreesC. Gastrocnemius CytOx activity in T-c=38.0degreesC (83.5 +/- 5.5 muatoms O.min(-1).g wet wt(-1)) was greater than all other groups (P < 0.05), exceeding sedentary (n = 7) by 73.2%. T-c of 40.4 and 39.2 degrees C also were higher than sedentary by 22.4 and 37.4%, respectively (P < 0.05). Quantification of CytOx content verified that the increased activity was due to an increase in protein content. In extensor digitorum longus, a nonactive muscle, CytOx was not elevated in T-c = 38.0degreesC. mtHSP70 was significantly elevated in gastrocnemius of T-c = 38.0degreesC compared with sedentary (P < 0.05) but was not elevated in extensor digitorum longus (P > 0.05). The data indicate that decreasing exercise T-c may enhance mitochondrial biogenesis and that mtHSP70 expression is not dependent on temperature.