Effects of concentric and eccentric contractions on phosphorylation of MAPKerk1/2 and MAPKp38 in isolated rat skeletal muscle

Open Access
Publisher Website
Google Scholar
Abstract
1 Exercise and contractions of isolated skeletal muscle induce phosphorylation of mitogen-activated protein kinases (MAPKs) by undefined mechanisms. The aim of the present study was to determine exercise-related triggering factors for the increased phosphorylation of MAPKs in isolated rat extensor digitorum longus (EDL) muscle. 2 Concentric or eccentric contractions, or mild or severe passive stretches were used to discriminate between effects of metabolic/ionic and mechanical alterations on phosphorylation of two MAPKs: extracellular signal-regulated kinase 1 and 2 (MAPKerk1/2) and stress-activated protein kinase p38 (MAPKp38). 3 Concentric contractions induced a 5-fold increase in MAPKerk1/2 phosphorylation. Application of the antioxidants N-acetylcysteine (20 mM) or dithiothreitol (5 mM) suppressed concentric contraction-induced increase in MAPKerk1/2 phosphorylation. Mild passive stretches of the muscle increased MAPKerk1/2 phosphorylation by 1.8-fold, whereas the combination of acidosis and passive stretches resulted in a 2.8-fold increase. Neither concentric contractions, nor mild stretches nor acidosis significantly affected phosphorylation of MAPKp38. 4 High force applied upon muscle by means of either eccentric contractions or severe passive stretches resulted in 5.7- and 9.5-fold increases of phosphorylated MAPKerk1/2, respectively, whereas phosphorylation of MAPKp38 increased by 7.6- and 1.9-fold (not significant), respectively. 5 We conclude that in isolated rat skeletal muscle an increase in phosphorylation of both MAPKerk1/2 and MAPKp38 is induced by mechanical alterations, whereas contraction-related metabolic/ionic changes (reactive oxygen species and acidosis) cause increased phosphorylation of MAPKerk1/2 only. Thus, contraction-induced phosphorylation can be explained by the combined action of increased production of reactive oxygen species, acidification and mechanical perturbations for MAPKerk1/2 and by high mechanical stress for MAPKp38.