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Figure 5 Involvement of epidermal growth factor receptor (EGFR) and Pyk2 in 4-aminopyridine (4-AP)-induced extracellular signal-regulated kinase (ERK) activation. (A, B) Cardiomyocytes were pre-incubated with either KN62 (KN [calmodulin kinase II and IV inhibitor]) (10 µmol/l), AG1478 (AG [epidermal growth factor inhibitor]) (250 nmol/l), cytochalasin D (CyD [actin dimerization inhibitor]) (10 µmol/l), calphostin C (Cal [PKC inhibitor]) (1 µmol/l) or calmidazolium (CMZ [calmodulin inhibitor]) (50 µmol/l) for 30 min and then treated with 4-AP for 15 min. Leukemia inhibitory factor (LIF) was used as a positive control. AG1478 and cytochalasin D strongly blocked 4-AP-induced ERK activation, whereas the other agents did not. (C) Densitometric analysis of the inhibitor experiment. Representative blot analyses are shown. All experiments were repeated at least five times and yielded similar results. Data are presented as the mean value ± SE. *p < 0.01 vs. 4-AP alone.