Prior serum- and AICAR-induced AMPK activation in primary human myocytes does not lead to subsequent increase in insulin-stimulated glucose uptake

Exposing isolated rat skeletal muscle to 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside [AICAR, a pharmacological activator of AMP-activated protein kinase (AMPK)] plus serum leads to a subsequent increase in insulin-stimulated glucose transport ( Fisher JS, Gao J, Han DH, Holloszy JO, and Nolte LA. Am J Physiol Endocrinol Metab 282: E18 - E23, 2002). Our goal was to determine whether preincubation of primary human skeletal muscle cells with human serum and AICAR ( Serum + AICAR) would also induce a subsequent elevation in insulin-stimulated glucose uptake. Cells were preincubated for 1 h under 4 conditions: 1) without AICAR or serum ( Control), 2) with serum, 3) with AICAR, or 4) with Serum + AICAR. Some cells were then collected for immunoblot analysis to assess phosphorylation of AMPK (pAMPK) and its substrate acetyl-CoA carboxylase (ACC). Other cells were incubated for an additional 4 h without AICAR or serum and then used to measure basal or insulin-stimulated 2-deoxyglucose (2-DG) uptake. Level of pAMPK was increased ( P < 0.01) for myotubes exposed to Serum + AICAR vs. all other groups. Phosphorylated ACC (pACC) levels were higher for both Serum + AICAR ( P < 0.05) and AICAR ( P < 0.05) vs. Control and Serum groups. Basal ( P < 0.05) and 1.2 nM insulin-stimulated ( P < 0.005) 2-DG uptake was higher for Serum vs. all other preincubation conditions at equal insulin concentration. Regardless of insulin concentration ( 0, 1.2, or 18 nM), 2-DG was unaltered in cells preincubated with Serum + AICAR vs. Control cells. In contrast to results with isolated rat skeletal muscle, increasing the pAMPK and pACC in human myocytes via preincubation with Serum + AICAR was insufficient to lead to a subsequent enhancement in insulin-stimulated glucose uptake.