Differential activation of mitogen-activated protein kinase signalling pathways by isometric contractions in isolated slow- and fast-twitch rat skeletal muscle

Activation of mitogen-activated protein (MAP) kinases has been implicated i n the signal transduction pathways linking exercise to adaptive changes of muscle protein expression. In the present study, we investigated whether co ntractions of isolated muscles induced phosphorylation of extracellular sig nal-regulated kinase 1 and 2 (ERK1/2) and p38 MAPK in a fibre-type dependen t manner. Slow-twitch (soleus) and fast-twitch (epitrochlearis, extensor di gitorum longus) rat skeletal muscles were exposed to intermittent tetanic s timulation. Compared with the contralateral non-stimulated muscle, contract ions increased ERK1/2 phosphorylation to the same extent in fast- and slow- twitch muscles. Significant increase in phosphorylation of p38 MAPK was obs erved in the fast-twitch muscles only. The total amount of ERK1/2 and p38 M APK proteins was higher in the slow-twitch soleus muscle. In conclusion, MA P kinase signalling pathways are differentially activated and expressed in slow- and fast-twitch muscles, in addition, this activation is owing to mus cle contraction per se and do not demand additional external influence.