Uptake of enalapril and expression of organic anion transporting polypeptide 1 in zonal, isolated rat hepatocytes

Sinusoidal entry is the first obligatory process preceding intracellular dr ug removal in liver. Transport of the angiotensin converting enzyme inhibit or enalapril (1-750 mu M with [H-3]enalapril), a substrate of Oatp1, the so dium-independent organic anion transporting polypeptide 1 cloned from rat l iver, was studied in rat hepatocytes isolated from all zones of the liver ( homogeneous) and from enriched periportal (PP) and perivenous (PV) hepatocy tes prepared by collagenase perfusion and zone-selective destruction with d igitonin, respectively. Uptake was linear over 1 min and was concentration- dependent. Transport by the homogeneous hepatocytes (in the presence and ab sence of Na+) and PP and PV cells was described by single saturable compone nts of similar kinetic constants (K-m values of 344-461 mu M and V-max valu es of 9.5-11.6 nmol/min/10(6) cells; P > .05, ANOVA). The K-m value for ena lapril uptake in hepatocytes was of the same order of magnitude compared wi th that for Oatp1 expressed in HeLa cells transfected with cDNA-Oatp1 and W estern blot analysis revealed similar levels of immunoreactive Oatp1 expres sion in PP and PV hepatocytes. However, enalapril was not taken up by Oatp2 nor by the human OATP expressed in recombinant vaccinia systems.