Hepatic uptake of cholecystokinin octapeptide by organic anion-transporting polypeptides OATP4 and OATP8 of rat and human liver

Background & Aims: Cholecystokinin (CCK) is a major gastrointestinal peptide hormone that is released postprandially from the small intestine and exerts marked effects on gallbladder and gastrointestinal motility. The smaller isoforms CCK-8 and CCK-4 are rapidly taken up into hepatocytes, metabolized, and excreted into bile. Our aim was to identify and characterize the hepatocellular CCK-8 uptake system. Methods: CCK-8 uptake was measured in Xenopus laevis oocytes expressing the organic anion-transporting polypeptides of rat liver (Oatp1,, Oatp2, Oatp3, or Oatp4) and of human liver (OATP-A, OATP-B, OATP-C, or OATP8) and in primary cultured rat hepatocytes. Results. Rat Oatp4 and human OATP8 efficiently mediated CCK-8 uptake in oocytes, with Michaelis constant (K-m) values of 14.9 +/- 2.9 mu mol/L and 11.1 +/- 2.9 mu mol/L, respectively. CCK-8 uptake by hepatocytes was also saturable, with a K-m of 6.7 +/- 2.1 mu mol/L. The K-m value in rat hepatocytes is consistent with Oatp4-mediated transport. Conclusions: CCK-8 is selectively transported by rat Oatp4 and human OATP8, both of which are exclusively expressed at the basolateral membrane of hepatocytes. These 2 transporters are the first and probably the predominant hepatic uptake systems for CCK-8 and may be critical for the rapid clearance of this hormone from the circulation.