(A) Stable mixed clonal N2A cells expressing the wildtype or one of the mutants were treated with vehicle or U50,488H (10 μM) for 30 min, harvested and receptor proteins were purified and resolved with SDS-PAGE. Immunoblotting was performed with the indicated antibodies. Membranes were stripped and re-blotted with anti-FLAG antibodies for total KOPR. (B) Staining intensity of each phosphorylated KOPR was normalized against that of the total KOPR in the same lane. Data were then normalized to those of 10 μM U50,488H-treated wildtype group and each value represents the mean ± S.E.M of 3 independent experiments. Data were analyzed by one-way ANOVA followed by Newman-Keuls post-hoc test. (**:p<0.01, ***:p<0.001, ****:p<0.0001, compared to U50,488H-treated group).