Читать книгу Drug Transporters - Группа авторов - Страница 22

An absorptive transporter does not necessarily mean that it influxes a substrate. Similarly, a secretory transporter does not have to be an efflux pump. For example, organic anion transporter OAT1, present at the basolateral membrane of the kidney proximal tubule, is an influx transporter based on its role of taking up drugs from the blood into the proximal tubule cells for their subsequent exit across the apical membrane into the urine for elimination. However, considering its overall role of removing drugs out of the blood circulation into the urine, OAT1 is a secretory transporter. Intestinally expressed organic anion‐transporting polypeptide 1A2 (OATP1A2) is localized on the apical domain of enterocytes. It can take up (i.e., influx) orally administered drugs into the enterocytes for their subsequent exit across the basolateral membrane into the blood stream, so OATP1A2 is considered an absorptive transporter. Therefore, influx transporters can function as either absorptive or secretory transporters depending on the tissue and on the membrane domain where they are expressed.