The α-subunit of AMPK is essential for submaximal contraction-mediated glucose transport in skeletal muscle in vitro

Abstract

AMP-activated protein kinase (AMPK) is a key signaling protein in the regulation of skeletal muscle glucose uptake, but its role in mediating contraction-induced glucose transport is still debated. The effect of contraction on glucose transport is impaired in EDL muscle of transgenic mice expressing a kinase-dead, dominant negative form of the AMPKα2subunit (KD-AMPKα2mice). However, maximal force production is reduced in this muscle, raising the possibility that the defect in glucose transport was due to a secondary decrease in force production and not impaired AMPKα2activity. Generation of force-frequency curves revealed that muscle force production is matched between wild-type (WT) and KD-AMPKα2mice at frequencies ≤50 Hz. Moreover, AMPK activation is already maximal at 50 Hz in muscles of WT mice. When EDL muscles from WT mice were stimulated at a frequency of 50 Hz for 2 min (200-ms train, 1/s, 30 volts), contraction caused an ∼3.5-fold activation of AMPKα2activity and an ∼2-fold stimulation of glucose uptake. Conversely, whereas force production was similar in EDL of KD-AMPKα2animals, no effect of contraction was observed on AMPKα2activity, and glucose uptake stimulation was reduced by 50% ( P < 0.01) As expected, 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranosyl 5′-monophosphate (AICAR) caused a 2.3-fold stimulation of AMPKα2activity and a 1.7-fold increase in glucose uptake in EDL from WT mice, whereas no effect was detected in muscle from KD-AMPKα2mice. These data demonstrate that AMPK activation is essential for both AICAR and submaximal contraction-induced glucose transport in skeletal muscle but that AMPK-independent mechanisms are also involved.