Fluorescence micrographs of 48 hpf zebrafish embryos that had been incubated with 0.5 μM rhodamine B or 1.0 μM calcein-am either in the presence of different ABC transporter inhibitors (A) or upon knock-down of Abcb4 or Abcb5 (B). ABC transporter inhibitor compounds were cyclosporin A (CsA), PSC833 and MK571. Morpholino oligonucelotides were used for knock-down of Abcb4 (Abcb4-SP-MO/Abcb4-ATG-MO) or Abcb5 (Abcb5-SP-MO). Exposure water of control embryos contained dye only (ctrl, ctrl-MO). The morpholino control (ctrl-MO) served to exclude unspecific morpholino effects on dye accumulation in the embryos. Brighter appearing embryos indicate accumulation of higher amounts of dye in the embryo tissue.