Amylin-mediated inhibition of insulin-stimulated glucose transport in skeletal muscle

Abstract

We examined the effects of amylin on 3- O-methyl-d-glucose (3- O-MG) transport in perfused rat hindlimb muscle under hyperinsulinemic (350 μU/ml, 2,100 pmol/l) conditions. Amylin at 100 nmol/l concentration inhibited 3- O-MG transport relative to control in all three basic muscle fiber types. Transport decreased in slow-twitch oxidative (from 5.65 ± 1.13 to 3.46 ± 0.71 μmol ⋅ g−1 ⋅ h−1), fast-twitch oxidative (from 6.84 ± 0.90 to 4.84 ± 0.76 μmol ⋅ g−1 ⋅ h−1), and fast-twitch glycolytic (from 1.27 ± 0.20 to 0.60 ± 0.05 μmol ⋅ g−1 ⋅ h−1) muscle. Amylin inhibition of insulin-stimulated glucose transport in skeletal muscle was accompanied by a 433 ± 72% increase in intracellular glucose 6-phosphate (G-6- P) despite the absence of extracellular glucose. The source of hexose units for the formation and maintenance of G-6- P was likely glycogen. Amylin increased glycogenolysis, increased lactate formation, and decreased glycogen synthase activity. Furthermore, the kinetics of glycogen synthase suggest that this enzyme may control intracellular G-6- P concentration. Despite the large increase in G-6- P, no detectable increase in uridine diphosphate- N-acetylhexosamines occurred, suggesting that the proposed glucosamine pathway may not be involved in transport inhibition. However, decreases in uridine diphosphate hexoses were detected. Therefore, uridine or hexosamine-based metabolites may be involved in amylin action.