The AMP-activated kinase (AMPK) functions as a fuel gauge and couples metabolism and cellular functions. In case of ATP-depletion AMPK is activated, which stimulates glucose uptake, glycolysis, lipolysis and ATP generation. In vivo studies have shown that chemical activation of AMPK improves blood glucose concentrations and lipid profiles. We therefore invesigated direct effects of AMPK activation or inhibition on insulin secretion and proliferation on INS-1E rat insulinoma cells. In whole-cell perforated-patch clamp experiments under high glucose KATP currents were significantly inhibited by the AMPK activator AICAR and [Ca²⁺]I showed an oscillating increase. Insulin secretion measured by ELISA was stimulated by AICAR within 1 h but significantly decreasd over 24 h. Cell proliferation and caspase activation were unaffected by the drug within 48h. Inhibition of AMPK by 6-[4-(2-piperidin-1-ylethoxy)phenyl]-3-pyridin- 4-ylpyrazolo[1,5-a]pyrimidine (compound C) significantly decreased insulin release and cell proliferation and induced caspase activation within 24–48 h. Our data imply that AICAR acutely stimulates insulin release via membrane depolarization and an incrase of [Ca²⁺]_I and that prolonged inhibition of AMPK induces apoptosis of INS-1E cells.