AMP kinase expression and activity in human skeletal muscle: effects of immobilization, retraining, and creatine supplementation.

The effects of leg immobilization and retraining in combination with oral creatine intake on muscle AMP-activated protein kinase (AMPK) protein expression and phosphorylation status were investigated. A double-blind trial was performed in young healthy volunteers (n = 22). A cast immobilized the right leg for 2 wk, whereafter the knee-extensor muscles of that leg were retrained for 6 wk. Half of the subjects received creatine monohydrate throughout the study (Cr; from 15 g down to 2.5 g daily), and the others ingested placebo (P; maltodextrin). Before and after immobilization and retraining, needle biopsies were taken from the right and left vastus lateralis muscles. In the right leg of P and Cr, immobilization did not affect AMPK alpha1-, alpha2-, and beta2-subunit expression or AMPK alpha-subunit phosphorylation status. However, irrespective of the treatment received, retraining increased the degree of alpha-subunit phosphorylation by approximately 25% (P <0.05) and increased AMPK alpha1-subunit expression (P <0.05) in both groups. From the start to the end of the study, AMPK subunit protein expression and alpha-subunit phosphorylation status were unchanged in the contralateral control leg. It is concluded that immobilization-induced muscle inactivity for 2 wk does not alter AMPK alpha1-, alpha2-, and beta2-subunit expression or alpha-AMPK phosphorylation status. Furthermore, the present observations indicate that AMPK probably is not implicated in the previously reported beneficial effects of oral creatine supplementation on muscle during immobilization and rehabilitative weight training.