Fig. 2. ( A ) The time course of the KCl-induced activation of MAP kinase. ( B ) The effects of EGTA and calcium channel blockers on the KCl-induced activation of mitogen-activated protein (MAP) kinase. PC12 cells were stimulated with 50 μM KCl for the indicated periods of time or with KCl for 2 min at 37°C after pretreatment with 1 mM EGTA, 2 mM ω-conotoxin GIVA, or 5 mM nifedipine for 5 min. The MAP kinase activity was detected as described in Materials and Methods. Protein blots were probed with phosphospecific Elk1 antibody. Typical results of three independent experiments are shown. ( C ) A densitmetric analysis of the MAP kinase activity. Activation is expressed as a percentage of the activation caused by 50 mM KCl without pretreatment (positive control). Values are mean ± SEM of three independent experiments. *Different form positive control at P < 0.05.