Regulation of 5′AMP-activated protein kinase activity and substrate utilization in exercising human skeletal muscle

Abstract

The metabolic role of 5ЈAMP-activated protein kinase (AMPK) in regulation of skeletal muscle metabolism in humans is unresolved. We measured isoform-specific AMPK activity and ␤-acetyl-CoA carboxylase (ACC␤) Ser 221 phosphorylation and substrate balance in skeletal muscle of eight athletes at rest, during cycling exercise for 1 h at 70% peak oxygen consumption, and 1 h into recovery. The experiment was performed twice, once in a glycogen-loaded (glycogen concentration ϳ900 mmol/kg dry wt) and once in a glycogendepleted (glycogen concentration ϳ160 mmol/kg dry wt) state. At rest, plasma long-chain fatty acids (FA) were twofold higher in the glycogen-depleted than in the loaded state, and muscle ␣1 AMPK (160%) and ␣2 AMPK (145%) activities and ACC␤ Ser 221 phosphorylation (137%) were also significantly higher in the glycogen-depleted state. During exercise, ␣2 AMPK activity, ACC␤ Ser 221 phosphorylation, plasma catecholamines, and leg glucose and net FA uptake were significantly higher in the glycogen-depleted than in the glycogen-loaded state without apparent differences in muscle high-energy phosphates. Thus exercise in the glycogen-depleted state elicits an enhanced uptake of circulating fuels that might be associated with elevated muscle AMPK activation. It is concluded that muscle AMPK activity and ACC␤ Ser 221 phosphorylation at rest and during exercise are sensitive to the fuel status of the muscle. During exercise, this dependence may in part be mediated by humoral factors.acetyl-CoA carboxylase; glycogen; fatty acids; catecholamines IN HUMANS, 5ЈAMP-ACTIVATED PROTEIN KINASE (AMPK) is stimulated in skeletal muscle during exercise, and the degree of activation is dependent on the exercise intensity (5,14,32,59). In rodent muscle, pharmaceutical activation of AMPK by 5-aminoimidazole-4-carboxamide (AICA)-riboside leads to GLUT4 recruitment to the surface membrane and a stimulation of glucose transport that is additive to the effect of insulin but not to contraction (22,28). In addition, contraction-stimulated glucose transport and AMPK activity covary with time in incubated skeletal muscle (33). On the basis of these findings, it is hypothesized that AMPK is a mediator of contraction-stimulated glucose transport (16,22,28). However, recent studies in muscle from mice that express a dominant inhibitory mutant of ␣-AMPK show that a substantial part of contraction-induced glucose transport in vitro is AMPK independent, whereas AICA-riboside-and hypoxia-induced transport is totally dependent on AMPK activation (31, 45). In accordance, rodent studies have revealed conditions under which muscle glucose transport by these stimuli is increased in response to contraction without concurrent AMPK activation (10). Furthermore, energy-depleting stimuli, such as 2,4-dinitrophenol and hyperosmolarity, increase AMPK activity and glucose transport in L6 cells and skeletal muscle (21,40). However, the increase in glucose transport, but not the AMPK activation, is inhibited by calcium chelation and protein kinase C inhibition ...

New strategies in sport nutrition to increase exercise performance

“…Indeed substantial experimental evidence in humans supports this. For example, when exercise is commenced in the glycogen depleted state the phosphorylation of AMPK is greater in the post exercise recovery when muscle glycogen is low [21][22][23]. Interestingly, in rodent studies when exercise occurs in the low glycogen state AMPK nuclear content is increased [24].…”

AMPKα2deficiency uncovers time dependency in the regulation of contraction-induced palmitate and glucose uptake in mouse muscle

“…During states of low energy, such as muscle contraction or exercise, it is widely accepted that liver kinase B1 (LKB1) acts as an upstream AMPK kinase that phosphorylates and activates AMPK and initiates a multitude of signaling events to maintain energy homeostasis (39 -41). Although strong evidence indicates that the LKB1-AMPK cascade is a key signaling pathway that regulates changes in glucose uptake, fatty acid (FA) uptake, and FA oxidation in contracting skeletal muscle (16,25,54,56), data also show that AMPK may not be the sole signal mediating contractioninduced changes in glucose uptake, FA uptake, and FA oxidation (35,36,56).Along with AMPK, mounting data suggest that increases in intracellular Ca 2ϩ concentration ([Ca 2ϩ ]) may play a key role in the regulation of glucose uptake, FA uptake, and FA oxidation in skeletal muscle and that this may occur in part via AMPK activation (3,28,51,53,56,57). There is evidence that Ca 2ϩ /calmodulin-dependent protein kinase (CaMK) kinase (CaMKK) activates AMPK in vitro in cells, whole skeletal muscle, and yeast (17,20,21,55), and we recently showed that activation of CaMKK and CaMKII leads to activation of AMPK in perfused rat hindlimbs (1, 35).…”

“…During states of low energy, such as muscle contraction or exercise, it is widely accepted that liver kinase B1 (LKB1) acts as an upstream AMPK kinase that phosphorylates and activates AMPK and initiates a multitude of signaling events to maintain energy homeostasis (39 -41). Although strong evidence indicates that the LKB1-AMPK cascade is a key signaling pathway that regulates changes in glucose uptake, fatty acid (FA) uptake, and FA oxidation in contracting skeletal muscle (16,25,54,56), data also show that AMPK may not be the sole signal mediating contractioninduced changes in glucose uptake, FA uptake, and FA oxidation (35,36,56).…”

Malonyl-CoA and carnitine in regulation of fat oxidation in human skeletal muscle during exercise

“…The ratio between fat and carbohydrate oxidation during exercise depends on preexercise substrate levels and exercise duration and intensity (12,40,42,44). However, the intracellular determinants of the use of these fuels are unclear.…”