Effect of inhibition of Src kinases on ERK1/2 activation. A-D: Hepatocytes were cultured for 3 h prior to preincubation for 30 min with timolol (10 μM) and the Src kinase inhibitors PP1 or PP2 at indicated concentrations in 0.5 % DMSO before stimulation for 5 min with norepinephrine (10 μM), PGF2α (10 μM), EGF (10 nM), thapsigargin (1 μM), or A23187 (10 μM). A: ERK1/2 activity, given as percent of untreated control, induced by hormonal agents expressed as the mean ± S.E.M. of four experiments after treatment with PP1 (10 μM). The inset shows an immunoblot of the effect of PP1 (20 μM) on thapsigargin-induced ERK1/2 response. B: A23187-induced ERK1/2 response after PP1 (10 μM) treatment. Results represent mean ± S.E.M of three experiments. C: Dose-response curve for the effect of PP2 on ERK1/2 activity induced by A23187. Results represent mean ± S.E.M of three experiments. All activity measurements (A-C) are expressed as percent of untreated control. D: Immunoblots showing the effect of PP1 (10 μM) or PP2 (10 μM) on ERK1/2 responses. Antibody against dually phosphorylated ERK1/2 was used.