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Figure 3. Comparison of the substrate specificity of human P-gp and zebrafish homologs. (A) Three-day cytotoxicity assays were performed with etoposide, doxorubicin or mitoxantrone on empty-vector-transfected HEK293 cells (Vector), HEK293 cells that express human P-gp (MDR-19), zebrafish Abcb4 (ZF Abcb4), or zebrafish Abcb5 (ZF Abcb5). (B) MDR-19, ZF Abcb4 and ZF Abcb5 cells were incubated with 500 nM BODIPY-ethylenediamine (EDA) in the presence or absence of 10 µM valspodar for 30 min. The medium was subsequently removed and replaced with substrate-free medium continuing without or with valspodar for another 1 h, after which intracellular fluorescence was measured on a flow cytometer.