MAPK Responses to a Repeated Exercise Bout in Skeletal Muscle

The adaptive changes seen in skeletal muscle after a single repeated bout are not understood at the molecular level. The activities of the mitogen activated protein kinases (MAPKs; ERK1/2, p38 and JNK) following two running bouts were studied in the biceps brachii of exercise naïve male mice (n=5) between 8 and 10 weeks of age. They ran two identical downhill treadmill bouts (−15°, 15 min, 25 m/min), separated by one week. MAPK activities were measured pre‐exercise (PE, control (−1 hr)), immediately before the second bout (pre2nd) and at eleven time points post second bout (post‐exercise, PX). After bout one, the activity of ERK1 decreased 2 fold relative to PE, ERK2 was unchanged, and p38 and JNK activities increased 3 and 8 fold above PE, respectively. Following the second bout of exercise, ERK1 activity decreased 2 to 6 fold below PE through 672 hr PX. ERK2 activity decreased 2 to 12 fold below PE, but initially decreased 14 fold below PE at 0 hr PX and 28 fold below PE at 168 hr PX. The activity of p38 decreased 2 fold below PE at 0.5 and 1 hr PX, increased between 2 and 7 fold below PE between 12 and 48 hr PX, thereafter returning to baseline. JNK activity generally increased between 0 to 6 hr PX (2 to 8 fold above PE) and then generally decreased 9 fold below PE from 24 to 168 hr PX. These data show a striking inhibition of ERK1 and ERK2 and in inverse relationship between p38 and JNK following a single repeated bout of exercise.