Fig. 1.

Phosphorylation of ERK1/2 by μOR agonists. (a) CHO cells stably expressing Flag-tagged μOR were treated for 5 min at 37°C with 10 μM of either ketamine, morphine, fentanyl, morphine + ketamine (1 : 1) or fentanyl + ketamine (1 : 1). (b) SK-N-SH cells that endogenously express μOR were treated for 5 min at 37°C with different concentrations (0–100 μM) of ketamine, morphine, ketamine + morphine (1 : 1), fentanyl, fentanyl + ketamine (1 : 1). (c) CHO cells stably expressing Flag-tagged μOR were treated with morphine or fentanyl (100 nM) in the absence or presence of 10 μM of μ-receptor antagonist, CTOP, for 5 min at 37°C. Cell lysates from panels a–c were subjected to western blot analysis using anti-phospho ERK1/2 and, anti-total ERK1/2 or anti-tubulin antibodies as described in Materials and methods section. Values were normalized to control cells not subjected to drug treatment. Results are the mean ± SE of six independent experiments in triplicates; values that represent significant differences from control by Dunnett’s test are indicated **p < 0.001.