Whole-body heat stress increases mitochondrial enzyme activity in mice skeletal muscle

Experimental Biology 2013

PURPOSE
The purposes of present study were to investigate i) the chronic effects of whole-body heat stress (WHS) on adaptation of mitochondrial enzyme activity and ii) the acute effects of WHS on kinase phosphorylation known to mediate mitochondrial biogenesis in mice skeletal muscle.

METHODS
ICR mice were divided into sedentary or WHS group. Mice in WHS group were exposed to hot environment chamber (30 × 20 × 13 cm, ambient temperature: 40 °C) for 30 min on each experiment day. In chronic experiment, we examined the effects of 3 weeks (Frequency: 5 days/week) WHS on maximal citrate synthase (CS) and 3-Hydroxyacyl-CoA dehydrogenase (3-HAD) activities in plantaris muscle. In acute experiment, we studied the effects of a single WHS on phosphorylation of AMP activated protein kinase (AMPK), p38 mitrogen activated protein kinase (p38 MAPK) and calcium/calmodulin-dependent protein kinase II (CaMK II) in plantaris muscle.

RESULTS
In chronic experiment, both maximal CS and 3-HAD activities were increased in WHS group (CS: +35%, P<0.01, 3-HAD: +49%, P<0.01). In acute experiment, phosphorylation of AMPK in WHS group was decreased (−43%, P<0.05). Phosphorylation of p38 MAPK was increased in WHS group (+252%, P<0.05). Phosphorylation of CaMK II was not different between groups.

CONCLUSION
Chronic whole-body heat stress increased mitochondrial enzyme activities.

Yuki Tamura, Yutaka Matsunaga, Hiroyuki Masuda, Yumiko Takahashi, Yuki Takahashi, Satoshi Takashima, Hidehiro Minagawa, Daisuke Hoshino, and Hideo Hatta