Fig. 3.

Time course of desensitization of opioid-induced ERK1/2 phosphorylation. SK-N-SH cells were treated with 10 μM of either morphine (a) or fentanyl (b) for different time periods (0–90 min) at 37°C in the absence or presence of ketamine (10 μM) and subjected to western blot analysis using anti-phospho ERK1/2 and anti-tubulin antibodies as described in Materials and methods section. Results are the mean ± SE of six independent experiments in triplicates.