AMP-activated protein kinase activity and glucose uptake in rat skeletal muscle

The AMP-activated protein kinase (AMPK) has been hypothesized to mediate co ntraction and 5-aminoimidazole-4-carboxamide 1-beta -D-ribonucleoside (AICA R)-induced increases in glucose uptake in skeletal muscle. The purpose of t he current study was to determine whether treadmill exercise and isolated m uscle contractions in rat skeletal muscle increase the activity of the AMPK alpha1 and AMPK alpha2 catalytic subunits in a dose-dependent manner and t o evaluate the effects of the putative AMPK inhibitors adenine 9-beta -D-ar abinofuranoside (ara-A), 8-bromo-AMP, and iodotubercidin on AMPK activity a nd 3-O-methyl-D-glucose (3-MG) uptake. There were dose-dependent increases in AMPK alpha2 activity and 3-MG uptake in rat epitrochlearis muscles with treadmill running exercise but no effect of exercise on AMPK alpha1 activit y. Tetanic contractions of isolated epitrochlearis muscles in vitro signifi cantly increased the activity of both AMPK isoforms in a dose-dependent man ner and at a similar rate compared with increases in 3-MG uptake. In isolat ed muscles, the putative AMPK inhibitors ara-A, 8-bromo-AMP, and iodotuberc idin fully inhibited AICAR-stimulated AMPK alpha2 activity and 3-MG uptake but had little effect on AMPK alpha1 activity, in contrast, these compounds had absent or minimal effects on contraction-stimulated AMPK alpha1 and -a lpha2 activity and 3-MG uptake. Although the AMPK alpha1 and -alpha2 isofor ms are activated during tetanic muscle contractions in vitro, in fast-glyco lytic fibers, the activation of AMPK alpha2-containing complexes may be mor e important in regulating exercise-mediated skeletal muscle metabolism in v ivo. Development of new compounds will be required to study contraction reg ulation of AMPK by pharmacological inhibition.