Contraction-mediated phosphorylation of AMPK is lower in skeletal muscle of adenylate kinase-deficient mice

The activity of AMP-activated protein kinase (AMPK) increases during muscle contractions as a result of elevated AMP concentration. We tested whether activation of AMPK would be altered during contractions in adenylate kinase (AK) 1-deficient (AK1(-/-)) mice, because they have a reduced capacity to form AMP. The right gastrocnemius-soleus-plantaris muscle group was stimulated via the sciatic nerve at 2 Hz for 30 min in both wild-type (WT) and AK1(-/-) animals. Initial force production was not different between the two groups (129.2 +/- 3.3 g vs. 140.9 +/- 8.5 g for WT and AK1(-/-), respectively); however, force production by AK1(-/-) mice was significantly greater over the 30-min stimulation period, and final tension was 85 +/- 4.5% of initial in WT and 102 +/- 3.2% of initial in AK1(-/-) mice. Western blot analysis showed that AMPK phosphorylation with contractions was clearly increased in WT muscles (4.0 +/- 1.1 above resting values), but did not change noticeably with AK deficiency (1.6 +/- 0.4 above WT resting values). However, increases in phosphorylation of acetyl CoA carboxylase were robust in both WT and AK1(-/-) muscles and not different between the two groups. These results suggest that reduced formation of AMP during contractions in skeletal muscle of AK1(-/-) mice results in reduced phosphorylation of AMPK. However, altered AMPK signaling was not apparent in the phosphorylation status of acetyl CoA carboxylase, a typical marker of AMPK activity.