Fetal bovine serum specific cell type. When changing from batch to batch it is usual to adapt the cells to the new batch of material, for example, by mixing 50% of the old serum with 50% of the new serum and allowing the cells to acclimatise to the new material. Serum is stored frozen to preserve the stability of components such as growth factors. When serum is thawed, some precipitation may be seen. This is a normal phenomenon and it does not compromise the quality of serum in any way. The precipitate may be removed by transferring the serum to sterile tubes and
P-glycoprotein lumen, in liver cells where it pumps them into bile ducts, in the cells of the proximal tubule of the kidney where it pumps them into urinary filtrate (in the proximal tubule), and in the capillary endothelial cells composing the blood–brain barrier and blood-testis barrier, where it pumps them back into the capillaries. P-gp is a glycoprotein that in humans is encoded by the "ABCB1" gene. P-gp is a well-characterized ABC-transporter (which transports a wide variety of substrates across extra- and intracellular membranes) of the MDR/TAP subfamily. The normal excretion of xenobiotics back into the gut lumen by P-gp pharmacokinetically