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Figure 3 Potassium channel blockers activate extracellular signal-regulated kinase (ERK) in cardiomyocytes. Cardiomyocytes were treated with (A) 4-aminopyridine (4-AP) (1 mmol/l), (B) E4031 (2 µmol/l), (C) tetraethylammonium (TEA) (10 mmol/l) and (D) quinidine (50 µmol/l) for the indicated times, and phosphorylation of ERK was detected by Western blot analysis. All potassium channel blockers induced phosphorylation of ERK, which peaked at 15 min. (E) Leukemia inhibitory factor (LIF) was used as a positive control agent. (F) 4-Aminopyridine caused dose-dependent augmentation of the phosphorylation of ERK in cardiomyocytes. The cells were treated with 0.01, 0.1 and 1 mmol/l of 4-AP for 15 min. All experiments were repeated at least four times and gave similar results.