Dose-dependent effects of metformin on mitochondrial respiration. (A) Total, (B) coupled and (C) uncoupled respiration in MCF7 cells after 24 hours of treatment with ddH2O (control) or metformin of varying concentrations (0.05, 0.5 and 5.0 mM). Fold change represents the change in respiration from untreated samples. (D) The fraction of mitochondrial respiration devoted to coupled and uncoupled respiration was calculated as in Figure 1. Data are presented as means ± SEM. n = 4 to 5. *P <0.05, One-way ANOVA followed by a Dunnet’s multiple comparison test.