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Figure 7 Effect of epidermal growth factor receptor (EGFR) deletion mutant on 4-aminopyridine (4-AP)-induced extracellular signal-regulated kinase (ERK) activation in cardiomyocytes. (Top) Cardiomyocytes were co-transfected with HA-tagged ERK2 and either deletion mutant of EGFR (pDN-EGFR), or empty plasmid (pcDNA), and treated with 4-AP for 15 min. The immunocomplex with anti-HA antibody was precipitated on protein A-sepharose, and in vitro myelin basic protein (MBP) kinase assay by ERK2 was performed, as described in Methods. Data are presented as the mean value ± SE of the results of five separate experiments determined by densitometry. (Bottom) Densitometric analysis of the inhibitory effect of dominant-negative EGFR on 4-AP-induced myelin basic protein kinase activity of ERK. Data are presented as the mean value ± SE. *p < 0.01 vs. 4-AP–treated cells transfected with the empty vector. pDN-EGFR = dominant negative EGFR plasmid.