ABCC4 and chronic kidney disease: Exposure of human kidney-2 cells (HK-2, a proximal tubule cell model) to sera obtained from rats with chronic renal failure (CRF) resulted in a significant downregulation of the protein expression levels of Oat3, organic anion-transporting polypeptide 1 (Oatp1), and P-gp, whereas levels of Mrp2, Mrp4, and Oatp2 were significantly upregulated [88].