Time course of cellular ⁵⁷Co-Cbl efflux from MRP1-deficient and control fibroblasts. (A) MRP1 levels in skin fibroblasts from Mrp1^(−/−) mice, MRP1 cDNA-transfected Mrp1^(−/−) mice and in WT skin fibroblast. The Western blots were probed with a MRP1-specific monoclonal antibody (top), before the blot was stripped and reprobed with an antibody against β-tubulin (bottom). The cellular protein loads are the same for each lane. (B) Time course of efflux of ⁵⁷Co-Cbl in the 3 cell types. The result is normalized to cellular protein content. (C) Cellular content of ⁵⁷Co-Cbl after efflux. The values are mean ± 1 SD of triplicate determinations.