Figure 1.

Effect of caffeine on contraction-stimulated AMPKα Thr¹⁷² phosphorylation and AMPK activity in incubated rat skeletal muscle. Isolated epitrochlearis muscle was preincubated and incubated for 30 min (A and C) or 120 min (B and D) in the absence (−) or presence (+) of 3 mmol/L caffeine. The muscle was tetanically contracted during the last 10 min of the incubation period and then subjected to western blot analysis (A and B) or an isoform-specific AMPK activity assay (C and D). Intracellular caffeine concentration was measured after incubation in the presence of 3 mmol/L caffeine for up to 120 min with or without electrical stimulation (E). Values are mean ± SE; n = 5–10 per group. *P < 0.05, **P < 0.01, ***P < 0.001 versus control; ^†P < 0.05, ^††P < 0.01, ^†††P < 0.001 versus contraction plus caffeine. AMPKα, 5′-Adenosine monophosphate-activated protein kinase α; NS, not significant.