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 biliru bin and sulfobromophthalein (BSP). Although other proteins have been s uggested as having bilirubin or BSP transport activity, these data hav e primarily been indirect, and their cloning and expression have not y et been accomplished. Although preliminary data suggest that organic a nion transporting polypeptide (oatp) accounts for a significant amount of BSP transport into the hepatocyte, there is certainly the possibil ity that other transporters exist. In addition, oatp appears to be a m ember of a new family of integral membrane transport proteins that may have overlapping substrate specificities. Organic anions such as bili rubin 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 lea rned recently regarding the mechanisms of organic anion transport. Thi s article will examine the history and current status of this field.