Figure 3. Extracellular signal-regulated kinase (ERK) activation by C6 glioma cell lines stably expressing mu, delta, and kappa opioid receptors. Cells were grown as described and then stimulated with 1-micro Meter concentrations of the indicated agonists for 30 min. Lysates were run on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, transferred, and probed with an anti-phospho ERK antibody recognizing the phosphorylated form of both ERK-1 (44 kD) and ERK-2 (42 kD). pERK 2, phosphorylated ERK protein control.