Hepatocellular uptake of cyclosporin A by simple diffusion.

Cyclosporin A is known to be eliminated mainly via the biliary++ pathway after biotransformation. Whether liver cells take up the drug by simple diffusion across the lipid barrier or by carrier-mediated transport, as shown for some other peptides, was unknown up to the present. Experiments with [3H]cyclosporin A on isolated rat hepatocytes indicate that the uptake of cyclosporin A is neither saturable nor is driven by metabolic energy. Cholestasis caused by cyclosporin A treatment is therefore not the result of mutual competition for a carrier protein. Nevertheless, cyclosporin A interacts with the bile acid transport system by non-competitive inhibition of bile salt uptake.