Aim: Recently it was reported that adenylate kinase-1 knockout mice (AK(-/-)) exhibit elevated rates of glucose uptake following repeated contractions and hypoxia, but the mechanism was not investigated. The purpose of the present study was to measure the changes in glucose transport and AMP-activated protein kinase (AMPK) phosphorylation/activity following repeated contractions in isolated muscles from AK(-/-) mice.
Methods: Extensor digitorum longus muscles underwent an intense stimulation protocol that decreased force to less than 10% of initial by the end of 10 min. Glucose uptake was measured with 2-deoxy-D-[1,2-(3)H]glucose.
Results: Muscle glucose uptake in the basal state was identical between control and AK(-/-) mice and increased twofold in both groups during contraction. The general antioxidant: N-acetylcysteine, decreased contraction-mediated glucose uptake by 30% in both groups. AMPK activity and phosphorylation were similar in the two groups in the basal state and, surprisingly, after contraction as well (approximately threefold increase). Both groups exhibited marked decreases in adenosine triphosphate following contraction (60-70% depletion), which coincided with stoichiometric increases in the content of inosine monophosphate, an indirect marker of AMP production. Adenylate kinase activity averaged 2081 +/- 106 micromol min(-1) (g dry wt)(-1) for control and 37 +/- 10 for AK(-/-) muscles; the activity in the AK(-/-) muscle is likely accounted for by isoforms other than AK1.
Conclusion: In conclusion, AK(-/-) mice have a normal capacity for contraction-mediated glucose uptake. This appears to occur via increases in AMP and reactive oxygen species that result in the activation of AMPK.