Effect of K⁺-channel blockade on ERK-2 activation. (A) Time-dependent activation of ERK-2 by FBS. Serum-starved ML-1 cells were left untreated or stimulated with FBS (10%). At the indicated time points, cells were collected and measured for ERK-2 activity and ERK-2 protein levels. (B) Effect of K⁺-channel blockade on FBS-induced ERK-2 activation in ML-1 cells. ML-1 cells were serum-starved and either untreated or stimulated with FBS (10%) for 15 minutes in the presence or absence of 2 mmol/L 4-AP. Cells were collected at the end of the treatment. ERK-2 activities protein levels were measured. (C) Time-dependent activation of ERK-2 by EGF in ML-1 cells. Serum-starved ML-1 cells were either untreated or stimulated with EGF (50 ng/mL). At the indicated time points, cells were collected and measured for ERK-2 activity and ERK-2 protein levels. (D) Effect of K⁺-channel blockade on EGF-induced ERK-2 activation in ML-1 cells. Serum-starved ML-1 cells were untreated or stimulated with EGF (50 ng/mL) for 15 minutes in the presence or absence of 2 mmol/L 4-AP. The cells were collected at the end of the treatment, and ERK-2 activities were measured. (E) Dose-dependent inhibitions of EGF-induced ERK-2 activation by K⁺-channel blockade with 4-AP. Serum-starved ML-1 cells were either untreated or stimulated with EGF (50 ng/mL) for 15 minutes in the presence of the indicated dosages of 4-AP. The cells were collected at the end of the treatment, and ERK-2 activities were measured.