AMPK and the Metabolic Actions of Metformin in Heart‐derived H9c2 cells

Abstract

Metformin stimulates glucose use and fatty acid oxidation in skeletal muscle and liver cells, reportedly via activation of AMP-activated protein kinase (AMPK). Whether the metabolic actions of metformin in heart muscle can be attributed to AMPK is not yet known with certainty. Thus, we set out to determine if metformin stimulates glucose use in heart muscle by activating AMPK. Lactate production and glucose use were measured in heart derived H9c2 cells with or without infection by adenovirus containing a dominant-negative mutant form of AMPK (DN-AMPK). AMPK activity was determined after immunoprecipitation from cell homogenates. Cells were exposed to Krebs-Henseleit solution containing substrates at physiological concentrations (5.5mM glucose, 0.4 mM palmitate) and 10−7 M insulin without (CON) or with metformin (MET) (2mM). Glucose use and lactate production were 1.7- and 2-fold greater in MET-treated cells than in CON cells, respectively (n=6 per group, P<0.05), and AMPK was activated by MET. DN-AMPK significantly reduced AMPK activity in H9c2 cells and abrogated the response of AMPK to metformin, but had no effect on glucose utilization or lactate production. Thus, these findings suggest that the metabolic actions of metformin in H9c2 cells are independent of AMPK activity and are mediated by other mechanisms. However, it is possible that residual AMPK activity is sufficiently large to stimulate glucose use and lactate production in response to metformin.