Bcl-x_Ldoes not prevent BCR-mediated desensitization of sustained, cycling ErkMAPkinase activation in WEHI-231 B cells. WEHI-231-Neo or -Bcl-x_L cells were stimulated with media, anti-IgM (1 μg/mL), or anti-IgM (1 μg/mL) plus anti-CD40 (10 μg/mL) for the time (h) indicated, up to 24 hours, and cell lysates were prepared. ErkMAPkinase activation was assessed by Western blot analysis of active, dually phosphorylated Erk and total Erk levels as described in “Materials and methods.” Data are representative of at least 10 experiments.