AMP-activated protein kinase (AMPK) is an important signaling effector that couples cellular metabolism and function. The effects of AMPK activation on pancreatic beta-cell function remain unresolved. We used 5-amino-imidazole carboxamide riboside (AICAR), an activator of AMPK, to define the signaling mechanisms linking the activation of AMPK with insulin secretion. Application of 300 mu M AICAR to mouse islets incubated in 5-14 mM glucose significantly increased AMPK activity and potentiated insulin secretion. AICAR inhibited ATP-sensitive K+ (K-ATP) channels and increased the frequency of glucose-induced calcium oscillations in islets incubated in 8-14 mM glucose. At lower glucose concentration (5 mM) AICAR did not affect K-ATP activity or intracellular ([Ca2+](i)). AICAR also did not inhibit Rb-86(+) efflux from islets isolated from Sur1(-/-) mice that lack K-ATP channels yet significantly potentiated glucose stimulated insulin secretion. Our data suggest that AICAR stimulates insulin secretion by both K-ATP channel-dependent and -independent pathways. (c) 2005 Elsevier Inc. All rights reserved.