Gastroenterology

Gastroenterology

Volume 120, Issue 2, February 2001, Pages 525-533
Gastroenterology

Liver, Pancreas, and Biliary Tract
Organic anion-transporting polypeptide B (OATP-B) and its functional comparison with three other OATPs of human liver☆☆

https://doi.org/10.1053/gast.2001.21176Get rights and content

Abstract

Background & Aims: Hepatic uptake of cholephilic organic compounds is mediated by members of the organic anion-transporting polypeptide (OATP) family. We aimed to characterize the novel OATP-B with respect to tissue distribution and hepatocellular localization and to compare its substrate specificity with those of OATP-A, OATP-C, and OATP8. Methods: Tissue distribution and hepatocellular localization of OATP-B were analyzed by Northern blotting and immunofluorescence, respectively. Transport of 16 substrates was measured for each individual human OATP in complementary RNA–injected Xenopus laevis oocytes. Results: Expression of OATP-B was most abundant in human liver, where it is localized at the basolateral membrane of hepatocytes. OATP-B, OATP-C, and OATP8 mediated high-affinity uptake of bromosulphophthalein (Km, ~0.7, 0.3, and 0.4 μmol/L, respectively). OATP-B also transported estrone-3-sulfate but not bile salts. Although OATP-A, OATP-C, and OATP8 exhibit broad overlapping substrate specificities, OATP8 was unique in transporting digoxin and exhibited especially high transport activities for the anionic cyclic peptides [d-penicillamine2,5]enkephalin (DPDPE; opioid-receptor agonist) and BQ-123 (endothelin-receptor antagonist). Conclusions: OATP-B is the third bromosulphophthalein uptake system localized at the basolateral membrane of human hepatocytes. OATP-B, OATP-C, and OATP8 account for the major part of sodium-independent bile salt, organic anion, and drug clearance of human liver.

GASTROENTEROLOGY 2001;120:525-533

Section snippets

Materials

All chemicals were of the highest degree of purity available and were readily available from commercial sources. [35S]BSP was synthesized at a specific activity of 9 Ci/mmol as described previously.19 [3H]Estrone-3-sulfate (53 Ci/mmol), [3H]estradiol-17β-glucuronide (44 Ci/mmol), [3H]dehydroepiandrosterone sulfate (DHEAS; 60 Ci/mmol), [3H]deltorphin II (41Ci/mmol), [3H]digoxin (19 Ci/mmol), [3H]enkephalin(2-d-penicillamin, 5-d-penicillamin; 45 Ci/mmol), [3H]ouabain (16.5 Ci/mmol), [3

Results

The full-length OATP-B cDNA coding for a 709–amino acid protein was isolated from a human brain cDNA library and contained a single serine (S)–to–phenylalanine (F) amino acid substitution at position 486 compared with the sequence published by Nagase et al.20 This substitution was also found by Tamai et al.18 The OATP-C and OATP8 cDNAs were isolated from a human liver cDNA library. Compared with the OATP-C sequence published by Abe et al.,14 there was a single asparagine (N)–to–aspartate (D)

Discussion

In this study we investigated the tissue distribution and hepatocellular localization of OATP-B, a novel member of the organic anion-transporting polypeptide family, and compared its spectrum of transport substrates with those of OATP-A, OATP-C, and OATP8 using a panel of 16 substrates previously shown to be transported by either OATP-A or by any of the rat Oatps. Northern blot analyses showed the highest level of OATP-B expression in liver, with additional expression in spleen, placenta, lung,

References (30)

Cited by (0)

☆☆

Supported by grants 32-59155.99 (to G.A.K.-U.), 31-59204.99 (to B.H.), and 31-045536.95 (to P.J.M.) from the Swiss National Science Foundation, Bern, Switzerland; grant KU 899/5-2 from the Deutsche Forschungsgemeinschaft, Bonn, Germany; and grant 99B30 from the Novartis Foundation for Biomedical Research, Basel, Switzerland.

3

fax: (41) 1-255 4411.

View full text