Twenty years of ATP-binding cassette (ABC) transporters.
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ATP-Binding Cassette Transporters↗
Biomedical subjects
Bruno Stieger
Publications and source records attributed to Bruno Stieger.
The bile salt export pump.
Canalicular secretion of bile salts mediated by the bile salt export pump Bsep constitutes the major driving force for the generation of bile flow. Bsep is a member of the B-family of the super family of ATP-binding cassette transporters and is classified as ABCB11. Bsep has a narrow substrate specificity, which is largely restricted to bile salts. Bsep is extensively regulated at the transcriptional and posttranscriptional level, which directly modulates canalicular bile formation. Pathophysiological alterations of Bsep by either inherited mutations or acquired processes such as inhibition by drugs or disease-related down regulation may lead to a wide spectrum of mild to severe forms of liver disease. Furthermore, many genetic variants of Bsep are known, some of which potentially render individuals susceptible to acquired forms of liver disease.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Characterization of two splice variants of human organic anion transporting polypeptide 3A1 isolated from human brain.
In the present study we isolated two splice variants of organic anion transporting polypeptide 3A1 (OATP3A1_v1 and OATP3A1_v2) from human brain. OATP3A1_v2 lacks 18 amino acids (aa) at the COOH-terminal end (692 aa) but is otherwise similar in sequence to OATP3A1_v1 (710 aa). OATP3A1_v1 exhibits a wide tissue distribution, with expression in testis, various brain regions, heart, lung, spleen, peripheral blood leukocytes, and thyroid gland, whereas OATP3A1_v2 is predominantly expressed in testis and brain. On the cellular and subcellular levels OATP3A1_v1 could be immunolocalized in testicular germ cells, the basolateral plasma membrane of choroid plexus epithelial cells, and neuroglial cells of the gray matter of human frontal cortex. Immunolocalization of OATP3A1_v2 included Sertoli cells in testis, apical and/or subapical membranes in choroid plexus epithelial cells, and neurons (cell bodies and axons) of the gray and white matter of human frontal cortex. The rodent ortholog Oatp3a1 was also widely distributed in rat brain, and its localization included somatoneurons as well as astroglial cells. Transport studies in cRNA-injected Xenopus laevis oocytes and in stably transfected Chinese hamster ovary FlpIn cells revealed a similar broad substrate specificity for both splice variants. Transported substrates include prostaglandin (PG)E(1) and PGE(2), thyroxine, and the cyclic oligopeptides BQ-123 (endothelin receptor antagonist) and vasopressin. These studies provide further evidence for the involvement of OATPs in oligopeptide transport. They specifically suggest that OATP3A1 variants might be involved in the regulation of extracellular vasopressin concentration in human brain and thus might influence the neuromodulation of neurotransmission by cerebral neuropeptides such as vasopressin.
Alprostadil↗
Hepatocyte transplantation: potential of hepatocyte progenitor cells and bone marrow derived stem cells.
The liver has a large regenerative capacity in response to injury. However, in severe cases of liver injury, its regenerative capacity may prove insufficent and the liver injury may progress to liver failure, and in such situations liver transplantation is the only treatment option. An alternative, less invasive approach may be transplantation of hepatocytes or hepatocyte precursor cells. In the adult liver two candidate progenitor cells have been identified: oval cells and small hepatocytes. The former are induced by liver injury under conditions preventing cell division of mature hepatocytes, while the latter are present in small numbers in normal liver. Both cell types have the capacity to expand and differentiate into hepatocytes. In recent years evidence has been presented that bone-marrow derived stem cells can also be expanded and differentiated into hepatocyte progenitor cells. Such cells may be a source for hepatocyte transplantation and hence have the potential to offer a novel therapy for liver failure.
Animals↗
Genetic variability, haplotype structures, and ethnic diversity of hepatic transporters MDR3 (ABCB4) and bile salt export pump (ABCB11).
Biliary excretion of bile salts and other bile constituents from hepatocytes is mediated by the apical (canalicular) transporters P-glycoprotein 3 (MDR3, ABCB4) and the bile salt export pump (ABCB11). Mutations in ABCB4 and ABCB11 contribute to cholestatic diseases [e.g., progressive familial intrahepatic cholestasis 2 (PFIC2), PFIC3, and intrahepatic cholestasis of pregnancy], and our objective was to establish genetic variability and haplotype structures of ABCB4 and ABCB11 in healthy populations of different ethnic backgrounds. All coding exons, 5 of 6 noncoding exons, 50 to 300 base pairs of the flanking intronic regions, and 2.5 to 2.8 kilobase pairs of the promoter regions of ABCB4 and ABCB11 were sequenced in 159 and 196 DNA samples of Caucasian, African-American, Japanese, and Korean origin. In total, 76 and 86 polymorphisms were identified in ABCB4 and ABCB11, respectively; among them, 14 and 28 exonic polymorphisms, and 8 and 10 protein-altering variants, of which 4 were predicted to have functional consequences. Both genes showed substantial ethnic differences with respect to allele number, frequency of common and population-specific sites, and patterns of linkage disequilibrium. Population genetic analysis suggested some selective pressure against changes in the protein, supporting the important endogenous role of these transporters. Haplotype variability was greater in ABCB11 than in ABCB4. An ABCB11 promoter haplotype was associated with significant decrease of activity compared with wild type. Our results contribute to a better understanding of the molecular basis and of ethnic differences in drug response, and provide a valuable tool for future research on the heredity of cholestatic liver injury.
5' Flanking Region↗
Bile salt toxicity aggravates cold ischemic injury of bile ducts after liver transplantation in Mdr2+/- mice.
Intrahepatic bile duct strictures are a serious complication after orthotopic liver transplantation (OLT). We examined the role of endogenous bile salt toxicity in the pathogenesis of bile duct injury after OLT. Livers from wild-type mice and mice heterozygous for disruption of the multidrug resistance 2 Mdr2 gene (Mdr2+/-) were transplanted into wild-type recipient mice. Mdr2+/- mice secrete only 50% of the normal amount of phospholipids into their bile, leading to an abnormally high bile salt/phospholipid ratio. In contrast to homozygous Mdr2-/- mice, the Mdr2+/- mice have normal liver histology and function under normal conditions. Two weeks after OLT, bile duct injury and cholestasis were assessed by light and electron microscopy, as well as through molecular and biochemical markers. There were no signs of bile duct injury or intrahepatic cholestasis in liver grafts from wild-type donors. Liver grafts from Mdr2+/- donors, however, had enlarged portal tracts with cellular damage, ductular proliferation, biliostasis, and a dense inflammatory infiltrate after OLT. Parallel to this observation, recipients of Mdr2+/- livers had significantly higher serum transaminases, alkaline phosphatase, total bilirubin, and bile salt levels, as compared with recipients of wild-type livers. In addition, hepatic bile transporter expression was compatible with the biochemical and histological cholestatic profile found in Mdr2+/- grafts after OLT. In conclusion, toxic bile composition, due to a high biliary bile salt/phospholipid ratio, acted synergistically with cold ischemia in the pathogenesis of bile duct injury after transplantation.
ATP Binding Cassette Transporter, Subfamily B↗
Interindividual variability of canalicular ATP-binding-cassette (ABC)-transporter expression in human liver.
Interindividual variability in hepatic canalicular transporter expression might predispose to the development of hepatic disorders such as acquired forms of intrahepatic cholestasis. We therefore investigated expression patterns of bile salt export pump (BSEP, ABCB11), multidrug resistance protein 3 (MDR3, ABCB4), multidrug resistance associated protein 2 (MRP2, ABCC2) and multidrug resistance protein 1 (MDR1, ABCB1) in healthy liver tissue of a white population. Protein expression levels were correlated with specific single nucleotide polymorphisms (SNPs) in the corresponding transporter genes. Hepatic protein expression levels from 110 individuals undergoing liver resection were assessed by Western blot analysis of liver plasma membranes enriched in canalicular marker enzymes. Each individual was genotyped for the following synonymous (s) and nonsynonymous (ns) SNPs: ABCB11: (ns:1457T>C and 2155A>G), ABCB4: (ns:3826A>G) and ABCC2 (ns:1286G>A,3600T>A and 4581G>A) and ABCB1 (ns:2677G>T/A and s:3435C>T). Transporter expression followed unimodal distribution. However, of all tested individuals 30% exhibited a high expression and 32% a low or very low expression phenotype for at least one of the four investigated transport proteins. Transporter expression levels did not correlate with age, sex, underlying liver disease, or presurgery medication. However, low BSEP expression was associated with the 1457C-allele in ABCB11 (P = .167) and high MRP2 expression was significantly correlated with the 3600A and 4581A ABCC2 variants (P = .006). In conclusion, the results demonstrate a considerable interindividual variability of canalicular transporter expression in normal liver. Furthermore, data suggest a polymorphic transporter expression pattern, which might constitute a risk factor for the development of acquired forms of cholestatic liver diseases.
ATP-Binding Cassette Transporters↗
Hepatocellular carcinoma in ten children under five years of age with bile salt export pump deficiency.
Hepatocellular carcinoma (HCC) is rare in young children. We attempted to see if immunohistochemical and mutational-analysis studies could demonstrate that deficiency of the canalicular bile acid transporter bile salt export pump (BSEP) and mutation in ABCB11, encoding BSEP, underlay progressive familial intrahepatic cholestasis (PFIC)--or "neonatal hepatitis" suggesting PFIC--that was associated with HCC in young children. We studied 11 cases of pediatric HCC in the setting of PFIC or "neonatal hepatitis" suggesting PFIC. Archival liver were retrieved and immunostained for BSEP. Mutational analysis of ABCB11 was performed in leukocyte DNA from available patients and parents. Among the 11 nonrelated children studied aged 13-52 months at diagnosis of HCC, 9 (and a full sibling, with neonatal hepatitis suggesting PFIC, of a tenth from whom liver was not available) had immunohistochemical evidence of BSEP deficiency; the eleventh child did not. Mutations in ABCB11 were demonstrated in all patients with BSEP deficiency in whom leukocyte DNA could be studied (n = 7). These mutations were confirmed in the parents (n = 14). With respect to the other 3 children with BSEP deficiency, mutations in ABCB11 were demonstrated in all 5 parents in whom leukocyte DNA could be studied. Thirteen different mutations were found. In conclusion, PFIC associated with BSEP deficiency represents a previously unrecognized risk for HCC in young children. Immunohistochemical evidence of BSEP deficiency correlates well with demonstrable mutation in ABCB11.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Quantitative microscopy reveals 3D organization and kinetics of endocytosis in rat hepatocytes.
In order to demonstrate the power of quantitative microscopy, the endocytic apparatus of rat hepatocytes was reexamined using in situ liver and short term cultured hepatocyte couplets that were allowed to internalize endocytic markers for various time intervals. Correlative confocal light and electron microscopy demonstrate a tubulovesicular reticulum representing the endocytic apparatus. Volume and membrane area account for 2% of cell volume and 30% plasma membrane surface. Colocalization analysis demonstrated that pathway-specific ligands and fluid-phase markers enter EEA1-positive vesicles, the early endosomal compartment, immediately after internalization. These vesicles are translocated rapidly from basolateral to perinuclear and apical locations. Ligands are sorted within 5 min to their respective pathways. Sequential colocalization of an asialoglycoprotein-pulse with rab7 and lamp3 demonstrates that early endosomes change into or fuse with late endosomes and lysosomes. Alternatively, markers are sequestered into the common endosome consisting of rab11-positive, long tubules that originate from early endosomes and show an affinity for the transcytotic marker pIgA and its receptor. This compartment mediates transcytosis by delivering the receptor-ligand complex to the subapical compartment, a set of apical, rab11-positive vesicles, which are connected to the tubular reticulum. We conclude that vesicular traffic between preexisting compartments, maturation or fusion of endocytic organelles, and transport in tubules act in concert and together mediate transport between compartments of a tubulovesicular endocytic apparatus. In addition, we show that quantitative microscopy using high resolution data sets can detect and characterize kinetics of various parameters thus adding a dynamic component to 3D information.
Animals↗
Tauroursodeoxycholic acid inserts the bile salt export pump into canalicular membranes of cholestatic rat liver.
Ursodeoxycholic acid exerts anticholestatic effects in chronic cholestatic liver disease in humans as well as in experimental animal models of cholestasis. Its taurine conjugate, TUDCA, was recently shown to stimulate insertion of the apical conjugate export pump, Mrp2 (ABCC2), into canalicular membranes of rat hepatocytes made cholestatic by exposure to taurolithocholic acid (TLCA). The aim of this immunoelectronmicroscopic study was to test whether TLCA and TUDCA modulate the canalicular density of the other key apical transporter, the bile salt export pump, Bsep (ABCB11), in a similar way. Immunoelectronmicroscopic analysis of Bsep density on canalicular membranes, microvilli, and pericanalicular area of hepatocytes was performed in rat liver tissue prepared after liver perfusion with bile acids or carrier medium only. TLCA (10 micromol/l for 50 min) decreased Bsep density in canalicular membranes to 31% of controls (P<0.05) when bile flow was reduced to 35% of controls (P<0.05). Concomitantly, Bsep density in a 1 microm pericanalicular zone increased to 202% (P<0.05) indicating effective retrieval of Bsep from the canalicular membrane induced by TLCA. Coadministration of TUDCA (25 micromol/l) led to a 3.2-fold increase of Bsep density in canalicular membranes equal to control liver (P<0.05 vs TLCA) in association with a 3.8-fold increase of bile flow (P<0.05 vs TLCA). Stimulation of apical membrane insertion of key transporters like the bile salt export pump, Bsep, and-as previously shown-the conjugate export pump, Mrp2, may contribute to the anticholestatic action of UDCA amides in cholestatic conditions.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Distribution and functional activity of P-glycoprotein and multidrug resistance-associated proteins in human brain microvascular endothelial cells in hippocampal sclerosis.
Multidrug resistance protein, also referred as P-glycoprotein (P-gp, MDR1; ABCB1) and multidrug resistance-associated protein (MRP) 1 (ABCC1) and 2 (ABCC2) are, thus far, candidates to cause antiepileptic drug (AED) resistance epilepsy. In this study, we investigated P-gp, MRP1 and MRP2 expression, localization and functional activity on cryosections and isolated human brain-derived microvascular endothelial cells (HBMEC) from epileptic patients (HBMEC-EPI) with hippocampal sclerosis (HS), as compared with HBMEC isolated from normal brain cortex (HBMEC-CTR). We examined the expression and distribution of three transporters, P-gp, MRP1 and MRP2 on two major parts of the resected tissue, the hippocampus and the parahippocampal gyrus (Gph). P-gp showed diffuse expression not only in endothelium but also by parenchymal cells in both the hippocampus and the Gph. MRP1 labeling was observed in parenchymal cells in the Gph. By contrast, MRP2 was mainly found in endothelium of the hippocampus. P-gp and MRP1 expression in the Gph was relatively high in the patient with long-term seizure history. Quantitative RT-PCR analysis of HBMEC revealed that MDR1, MRP1 as well as MRP5 (ABCC5) and MRP6 (ABCC6) were overexpressed in HBMEC-EPI at the mRNA level. HBMEC from both normal and epilepsy groups displayed protein expression of P-gp, whereas MRP1 and MRP2 were seen only in HBMEC-EPI. Accordingly, it is of particular interest that MRP functional activities were observed in HBMEC-EPI, but not in HBMEC-CTR. Our results suggest that complex MDR expression changes not only in the hippocampus but in the Gph may play a role in AED pharmacoresistance in intractable epilepsy patients with mesial temporal lobe epilepsy (MTLE) by altering the permeability of AEDs across the blood-brain barrier (BBB).
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Proteomic analysis of plasma membrane vesicles isolated from the rat renal cortex.
Polarized epithelial cells are responsible for the vectorial transport of solutes and have a key role in maintaining body fluid and electrolyte homeostasis. Such cells contain structurally and functionally distinct plasma membrane domains. Brush border and basolateral membranes of renal and intestinal epithelial cells can be separated using a number of different separation techniques, which allow their different transport functions and receptor expressions to be studied. In this communication, we report a proteomic analysis of these two membrane segments, apical and basolateral, obtained from the rat renal cortex isolated by two different methods: differential centrifugation and free-flow electrophoresis. The study was aimed at assessing the nature of the major proteins isolated by these two separation techniques. Two analytical strategies were used: separation by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) at the protein level or by cation-exchange high-performance liquid chromatography (HPLC) after proteolysis (i.e., at the peptide level). Proteolytic peptides derived from the proteins present in gel pieces or from HPLC fractions after proteolysis were sequenced by on-line liquid chromatography-tandem mass spectrometry (LC-MS/MS). Several hundred proteins were identified in each membrane section. In addition to proteins known to be located at the apical and basolateral membranes, several novel proteins were also identified. In particular, a number of proteins with putative roles in signal transduction were identified in both membranes. To our knowledge, this is the first reported study to try and characterize the membrane proteome of polarized epithelial cells and to provide a data set of the most abundant proteins present in renal proximal tubule cell membranes.
Amino Acid Sequence↗
Enterohepatic transport of bile salts and genetics of cholestasis.
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Animals↗
Impaired expression and function of the bile salt export pump due to three novel ABCB11 mutations in intrahepatic cholestasis.
BACKGROUND/AIMS: Inherited dysfunction of the bile salt export pump BSEP (ABCB11) causes a progressive and a benign form of familial intrahepatic cholestasis, denominated as PFIC2 and BRIC2, respectively. We functionally characterized novel ABCB11 mutations encountered in two patients with a PFIC2 and a BRIC2 phenotype, respectively. METHODS: BSEP expression was determined in liver biopsies by immunohistochemistry. ABCB11 mutations were functionally characterized by taurocholate transport in SF9 cells transfected with human ABCB11. RESULTS: The PFIC2 patient was compound heterozygous for a splicing mutation in intron 4 ((+3)A > C) combined with an early stop codon at position 930 (R930X), while the BRIC2 patient was compound heterozygous for two nonsynonymous mutations in exon 9 (E297G) and exon 12 (R432T), respectively. Hepatic BSEP expression was absent in PFIC2 and preserved in BRIC2. In BRIC2, taurocholate transport was decreased to 13% and 20% of reference levels for R432T and E297G, respectively. CONCLUSIONS: The intron 4 (+3)A > C, R930X and R432T represent previously undescribed mutations of the ABCB11 gene that confer a PFIC2 and a BRIC2 phenotype, respectively. By combining functional in-vitro characterization with immunohistochemical detection of variant BSEP we provide direct evidence for the role of ABCB11 mutations in the pathogenesis of different forms of intrahepatic cholestasis.
ATP Binding Cassette Transporter, Subfamily B, Mem↗
Magnetic resonance imaging with hepatospecific contrast agents in cirrhotic rat livers.
OBJECTIVE: During biliary cirrhosis in rats, organic anion-transporting peptides (Oatps) and ATP-dependent multidrug resistance-associated protein 2 (Mrp2) that are likely to transport the contrast agent Gd-BOPTA through hepatocytes are down-regulated. However, the consequences of such down-regulation on the signal intensity (SI) enhancement are unknown. Consequently, the aim of our study was to measure the hepatic SI enhancement during Gd-BOPTA perfusion as well as the Oatp and Mrp2 expression in normal and cirrhotic livers. MATERIALS AND METHODS: The hepatic SI enhancement during Gd-BOPTA perfusion was measured in livers isolated from normal rats and rats that had a bile duct ligation (BDL) 15, 30, and 60 days before the perfusion. Hepatic injury and transporter expression were measured in control and cirrhotic rats. RESULTS: BDL induced a severe hepatic injury that increased over time with a down-regulation of the transporter expression. The extracellular space (assessed by Gd-DTPA perfusion) increased with the severity of the disease. Gd-BOPTA-induced SI enhancement remained similar in BDL-15 and BDL-30 rats than in control rats but significantly decreased in severe cirrhosis (BDL-60 rats). In comparison, the Mn-DPDP-induced SI enhancement decreases proportionally to the severity of the disease. CONCLUSION: During biliary cirrhosis, Gd-BOPTA-induced SI enhancement could not be related to the hepatic expression of transporters.
ATP-Binding Cassette Transporters↗
Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver.
Hepatocytes and cholangiocytes release ATP into bile, where it is rapidly degraded into adenosine and P(i). In rat, biliary P(i) concentration (0.01 mM) is approximately 100-fold and 200-fold lower than in hepatocytes and plasma, respectively, indicating active reabsorption of biliary P(i). We aimed to functionally characterize canalicular P(i) reabsorption in rat liver and to identify the involved P(i) transport system(s). P(i) transport was determined in isolated rat canalicular liver plasma membrane (LPM) vesicles using a rapid membrane filtration technique. Identification of putative P(i) transporters was performed with RT-PCR from liver mRNA. Phosphate transporter protein expression was confirmed by Western blotting in basolateral and canalicular LPM and by immunofluorescence in intact liver. Transport studies in canalicular LPM vesicles demonstrated sodium-dependent P(i) uptake. Initial P(i) uptake rates were saturable with increasing P(i) concentrations, exhibiting an apparent K(m) value of approximately 11 muM. P(i) transport was stimulated by an acidic extravesicular pH and by an intravesicular negative membrane potential. These data are compatible with transport characteristics of sodium-phosphate cotransporters NaPi-IIb, PiT-1, and PiT-2, of which the mRNAs were detected in rat liver. On the protein level, NaPi-IIb was detected at the canalicular membrane of hepatocytes and at the brush-border membrane of cholangiocytes. In contrast, PiT-1 and PiT-2 were detected at the basolateral membrane of hepatocytes. We conclude that NaPi-IIb is most probably involved in the reabsorption of P(i) from primary hepatic bile and thus might play an important role in the regulation of biliary P(i) concentration.
Animals↗
Vectorial transport of bile salts across MDCK cells expressing both rat Na+-taurocholate cotransporting polypeptide and rat bile salt export pump.
Bile salts are predominantly taken up by hepatocytes via the basolateral Na(+)-taurocholate cotransporting polypeptide (NTCP/SLC10A1) and secreted into the bile by the bile salt export pump (BSEP/ABCB11). In the present study, we transfected rat Ntcp and rat Bsep into polarized Madin-Darby canine kidney cells and characterized the transport properties of these cells for eight bile salts. Immunohistochemical staining demonstrated that Ntcp was expressed at the basolateral domains, whereas Bsep was expressed at the apical domains. Basal-to-apical transport of taurocholate across the monolayer expressing only Ntcp and that coexpressing Ntcp/Bsep was observed, whereas the flux across the monolayer of control and Bsep-expressing cells was symmetrical. Basal-to-apical transport of taurocholate across Ntcp/Bsep-coexpressing monolayers was significantly higher than that across monolayers expressing only Ntcp. Kinetic analysis of this vectorial transport of taurocholate gave an apparent K(m) value of 13.9 +/- 4.7 microM for cells expressing Ntcp alone, which is comparable with 22.2 +/- 4.5 microM for cells expressing both Ntcp and Bsep and V(max) values of 15.8 +/- 4.2 and 60.8 +/- 9.0 pmol.min(-1).mg protein(-1) for Ntcp alone and Ntcp and Bsep-coexpressing cells, respectively. Transcellular transport of cholate, glycocholate, taurochenodeoxycholate, chenodeoxycholate, glycochenodeoxycholate, tauroursodeoxycholate, ursodeoxycholate, and glycoursodeoxycholate, but not that of lithocholate was also observed across the double transfectant. This double-expressing system can be used as a model to clarify vectorial transport of bile salts across hepatocytes under physiological conditions.
Adenoviridae↗
Small hepatocytes in culture develop polarized transporter expression and differentiation.
Rat small hepatocytes have been shown to proliferate in culture and to form organoids with differentiated hepatocytes in vitro. To evaluate the degree of polarized transporter differentiation of rat small hepatocytes during 9 weeks of culturing, we studied the time-dependent expression and subcellular localization of the major bile salt and organic anion transport systems of hepatocytes [i.e. the basolateral sodium-taurocholate co-transporting protein (Ntcp), organic-anion-transporting polypeptide 1b2 (Oatp1b2), the canalicular bile-salt export pump (Bsep) and multidrug-resistance-associated protein 2 (Mrp2)]. Small hepatocytes proliferated and differentiated in culture and formed sharply demarcated colonies as assessed by morphology, alpha-fetoprotein, albumin and Mrp1 expression. Polarized surface transporter expression was evident after 5 weeks of culturing for Ntcp, Oatp1b2 and Mrp2, and after 7 weeks for Bsep. After 9 weeks in culture, the vast majority of matured hepatocytes expressed Ntcp/Oatp1b2 at the basolateral and Bsep/Mrp2 at the canalicular plasma-membrane domains. This polarized transporter expression was accompanied by canalicular secretion of fluorescein-diacetate and cholylglycyl-fluorescein. Furthermore, an anastomizing three-dimensional network of bile canaliculi developed within piling-up colonies. These data demonstrate that cultured rat small hepatocytes acquire a fully differentiated transporter expression phenotype during their development into hepatic 'organoid-like' clusters of mature hepatocytes. Thereby, the time-dependent sequence of transporter expression mirrored the ontogenesis of transporter expression in developing rat liver, supporting the concept that small hepatocytes correspond to the hepatocyte lineage derived from embryonic hepatoblasts and/or from a different pool of 'committed hepatocyte progenitor cells'.
ATP Binding Cassette Transporter, Subfamily B, Mem↗