Abstract
Here the hypothesis that skeletal muscle Ca(2+)-calmodulin-dependent kinase II (CaMKII) expression and signalling would be modified by endurance training was tested. Eight healthy, young men completed 3 weeks of one-legged endurance exercise training with muscle samples taken from both legs before training and 15 h after the last exercise bout. Along with an approximately 40% increase in mitochondrial F(1)-ATP synthase expression, there was an approximately 1-fold increase in maximal CaMKII activity and CaMKII kinase isoform expression after training in the active leg only. Autonomous CaMKII activity and CaMKII autophosphorylation were increased to a similar extent. However, there was no change in alpha-CaMKII anchoring protein expression with training. Nor was there any change in expression or Thr(17) phosphorylation of the CaMKII substrate phospholamban with training. However, another CaMKII substrate, serum response factor (SRF), had an approximately 60% higher phosphorylation at Ser(103) after training, with no change in SRF expression. There were positive correlations between the increases in CaMKII expression and SRF phosphorylation as well as F(1)ATPase expression with training. After training, there was an increase in cyclic-AMP response element binding protein phosphorylation at Ser(133), but not expression, in muscle of both legs. Taken together, skeletal muscle CaMKII kinase isoform expression and SRF phosphorylation is higher with endurance-type exercise training, adaptations that are restricted to active muscle. This may contribute to greater Ca(2+) mediated regulation during exercise and the altered muscle phenotype with training.