Hepatocellular sinusoidal membrane organic anion transport and transporters

This review focuses on oatp, a rat liver protein that has been cloned on the basis of its ability to transport organic anions such as bilirubin and sulfobromophthalein (BSP). Although other proteins have been suggested as having bilirubin or BSP transport activity, these data have primarily been indirect, and their cloning and expression have not yet been accomplished. Although preliminary data suggest that organic anion transporting polypeptide (oatp) accounts for a significant amount of BSP transport into the hepatocyte, there is certainly the possibility that other transporters exist. In addition, oatp appears to be a member of a new family of integral membrane transport proteins that may have overlapping substrate specificities. Organic anions such as bilirubin and sulfobromophthalein (BSP) circulate bound tightly to albumin from which they are rapidly extracted by hepatocytes. This process of organic anion uptake has been the subject of extensive investigation over many years. Although details remain unresolved, much has been learned recently regarding the mechanisms of organic anion transport. This article will examine the history and current status of this field.