Abstract
Sinusoidal entry is the first obligatory process preceding intracellular drug removal in liver. Transport of the angiotensin converting enzyme inhibitor enalapril (1–750 μM with [3H]enalapril), a substrate of Oatp1, the sodium-independent organic anion transporting polypeptide 1 cloned from rat liver, was studied in rat hepatocytes isolated from all zones of the liver (homogeneous) and from enriched periportal (PP) and perivenous (PV) hepatocytes prepared by collagenase perfusion and zone-selective destruction with digitonin, respectively. Uptake was linear over 1 min and was concentration-dependent. Transport by the homogeneous hepatocytes (in the presence and absence of Na+) and PP and PV cells was described by single saturable components of similar kinetic constants (Kmvalues of 344–461 μM and Vmax values of 9.5–11.6 nmol/min/106 cells; P > .05, ANOVA). The Km value for enalapril uptake in hepatocytes was of the same order of magnitude compared with that for Oatp1 expressed in HeLa cells transfected with cDNA-Oatp1 and Western blot analysis revealed similar levels of immunoreactive Oatp1 expression in PP and PV hepatocytes. However, enalapril was not taken up by Oatp2 nor by the human OATP expressed in recombinant vaccinia systems.
Footnotes
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Send reprint requests to: Dr. K. S. Pang, Faculty of Pharmacy, University of Toronto, 19 Russell Street, Toronto, Ontario, Canada M5S 2S2. E-mail: ks.pang{at}utoronto.ca
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This work was supported by the Medical Research Council of Canada [MT15657, MOP36,457 (K.S.P.)], and the National Institutes of Health [DK23026, DK41296 (A.W.W.), and GM54724 (R.B.K.)], and a grant from the Merck Sharp and Dohme Research Laboratories, West Point, PA (K.S.P.).
- Abbreviations used are::
- ACEi
- angiotensin converting enzyme inhibitor
- BSP
- bromosulfophthalein
- Oatp1
- organic anion transporting polypeptide 1 cloned from rat liver
- OATP
- organic anion transporting polypeptide cloned from human liver
- PP
- periportal
- PV
- perivenous
- DIDS
- 4,4′-diisothiocyanostilbene-2, 2′-disulfonic acid
- Received December 28, 1999.
- Accepted March 22, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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Uptake of Enalapril and Expression of Organic Anion Transporting Polypeptide 1 in Zonal, Isolated Rat Hepatocytes
