Activation of AMPA and kainate receptors induces Bax upregulation, as well as Bax translocation to mitochondria and cytochrome c release, which are calpain dependent. Cultured oligodendrocytes were stimulated with AMPA (10 μm, plus 100 μm CTZ) or kainate (KA) (3 μm, plus 100 μm GYKI53655) for 15 min, with or without the calpain inhibitor PD150606 (100 μm). After 30 min, both total protein and mitochondrial or cytosolic fractions were extracted and analyzed by Western blotting with a specific antibody against Bax. A, Representative blots for Bax expression in total cell lysates obtained from oligodendrocytes treated with agonists. Quantification of the bands showed Bax upregulation as a consequence of AMPA and kainate receptor activation. β-Actin levels were measured as a normalization control. B, Western blot analysis of Bax expression in the mitochondrial fraction showed an increase triggered by AMPA and kainate receptor activation, which was abolished with the calpain inhibitor PD150606. The histogram illustrates the quantitative analysis and shows that agonists caused an elevation of up to 2.5-fold of the mitochondrial Bax level, compared with the control, and the presence of PD150606 prevented that increase. COX-IV levels were measured as a normalization control. C, Western blot analysis of Bax and cytochrome c in cytosolic fractions of oligodendrocytes treated with AMPA or kainate, alone or in combination with PD150606. Treatment with agonists induced a significant decrease in the cytosolic Bax expression level that was paralleled by an increase in the cytochrome c level. As shown by quantitative analysis, both changes were not precluded in the presence of the calpain inhibitor PD150606. β-Actin levels were measured as an internal cytosolic control. *p < 0.05, **p < 0.01, ***p < 0.001, compared with control; ^#p < 0.05, ^##p < 0.01, compared with cells treated with agonist alone.