Knockout of the α2 but not α1 5′-AMP-activated protein kinase isoform abolishes 5-aminoimidazole-4-carboxamide-1-β-4-ribofuranoside- but not contraction-induced glucose uptake in skeletal muscle

We investigated the importance of the two catalytic alpha-isoforms of the 5'-AMP-activated protein kinase (AMPK) in 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside ( AICAR) and contraction-induced glucose uptake in skeletal muscle. Incubated soleus and EDL muscle from whole-body alpha(2)- or alpha(1)-AMPK knockout (KO) and wild type (WT) mice were incubated with 2.0 mM AICAR or electrically stimulated to contraction. Both AICAR and contraction increased 2DG uptake in WT muscles. KO of alpha(2), but not alpha(1), abolished AICAR-induced glucose uptake, whereas neither KO affected contraction-induced glucose uptake. AICAR and contraction increased alpha(2)- and alpha(1)-AMPK activity in wild type (WT) muscles. During AICAR stimulation, the remaining AMPK activity in KO muscles increased to the same level as in WT. During contraction, the remaining AMPK activity in alpha(2)-KO muscles was elevated by 100% probably explained by a 2-3-fold increase in alpha(1)-protein. In alpha(1)-KO muscles, alpha(2)-AMPK activity increased to similar levels as in WT. Both interventions increased total AMPK activity, as expressed by AMPK-P and ACCbeta-P, in WT muscles. During AICAR stimulation, this was dramatically reduced in alpha(2)-KO but not in alpha1-KO, whereas during contraction, both measurements were essentially similar to WT in both KO-muscles. The results show that alpha(2)-AMPK is the main donor of basal and AICAR-stimulated AMPK activity and is responsible for AICAR-induced glucose uptake. In contrast, during contraction, the two alpha-isoforms seem to substitute for each other in terms of activity, which may explain the normal glucose uptake despite the lack of either alpha(2)- or alpha(1)-AMPK. Alternatively, neither alpha-isoform of AMPK is involved in contraction-induced muscle glucose uptake.