Fig. 3. (A) Effect of a 6 h treatment with 20 µM BAPTA-AM on the CREB-sensitive luciferase activity after transfection of L929 (black) or mtDNA-depleted L929 (hatched) cells with luciferase reporter genes driven by either CREB-regulated c-fos or α-inhibin promoters. Luciferase activity was determined and expressed as RLU after normalization for β-galactosidase activity (n = 6; ***, significantly different from mtDNA-depleted cells with P <0.001). (B) Intracellular calcium concentration ratio in L929 and mtDNA-depleted cells loaded with 10 µM Fluo-3-AM. Results are expressed in fold increase of control cells, and represent the mean ± SD for n = 3 (***, significantly different from L929 with P <0.001).