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

Abstract

AMP-activated protein kinase (AMPK) is a fuel sensor in skeletal muscle with multiple downstream signaling targets that may be triggered by increases in intracellular Ca2+concentration ([Ca2+]). The purpose of this study was to determine whether increases in intracellular [Ca2+] induced by caffeine act solely via AMPKα2and whether AMPKα2is essential to increase glucose uptake, fatty acid (FA) uptake, and FA oxidation in contracting skeletal muscle. Hindlimbs from wild-type (WT) or AMPKα2dominant-negative (DN) transgene mice were perfused during rest ( n = 11), treatment with 3 mM caffeine ( n = 10), or muscle contraction ( n = 11). Time-dependent effects on glucose and FA uptake were uncovered throughout the 20-min muscle contraction perfusion period ( P < 0.05). Glucose uptake rates did not increase in DN mice during muscle contraction until the last 5 min of the protocol ( P < 0.05). FA uptake rates were elevated at the onset of muscle contraction and diminished by the end of the protocol in DN mice ( P < 0.05). FA oxidation rates were abolished in the DN mice during muscle contraction ( P < 0.05). The DN transgene had no effect on caffeine-induced FA uptake and oxidation ( P > 0.05). Glucose uptake rates were blunted in caffeine-treated DN mice ( P < 0.05). The DN transgene resulted in a greater use of intramuscular triglycerides as a fuel source during muscle contraction. The DN transgene did not alter caffeine- or contraction-mediated changes in the phosphorylation of Ca2+/calmodulin-dependent protein kinase I or ERK1/2 ( P > 0.05). These data suggest that AMPKα2is involved in the regulation of substrate uptake in a time-dependent manner in contracting muscle but is not necessary for regulation of FA uptake and oxidation during caffeine treatment.