Bap31 and Fis1 mediate cytosolic calcium release and the effects of apoptosis-inducing drugs. (A) Baseline cytosolic calcium concentrations of three virally transduced stable cell lines were measured: pLKO SC (control cell line), pLKO Bap31 (Bap31 knockdown cells), and pLKO Fis1 (Fis1 knockdown cells). AU, arbitrary unit (B) Stable Bap31 knockdown cells were transfected either with β-gal or Fis1. The cytosolic calcium concentration was measured 48 h after transfection with Fluo-4/AM dye using FACS. The mean Fluo-4/AM fluorescent intensity of the β-gal-transfected cells were set to 100% as before. (C) Stable Bap31-downregulated cells (pLKO Bap31) were co-transfected with crBap31-mut and Fis1. The cytosolic calcium level was determined using Fluo-4/AM staining and FACS analysis. The mean calcium level of pLKO SC β-gal-transfected cells were set to 100%. (D, E) pLKO SC control cells and knockdown cells for Bap31 or Fis1 were treated with actinomycin D (C) or etoposide (D) at the indicated concentrations for 6 and 20 h, respectively, and the relative cytosolic calcium levels were measured using Fluo-4/AM dye and FACS analysis.