Characterization of an organic anion transport system in a placental cell line

Transporters within the placenta play a crucial role in the distribution of nutrients and xenobiotics across the maternal-fetal interface. An organic anion transport system was identified on the apical membrane of the rat placenta cell line HRP-1, a model for the placenta barrier. The apical uptake of 3H-labeled organic anion estrone sulfate in HRP-1 cells was saturable ( Km = 4.67 μM), temperature and Na+ dependent, Li+ tolerant, and pH sensitive. The substrate specificity of the transport system includes various steroid sulfates, such as β-estradiol 3,17-disulfate, 17β-estradiol 3-sulfate, and dehydroepiandrosterone 3-sulfate (DHEAS) but does not include taurocholate, p-aminohippuric acid (PAH), and tetraethylammonium. Preincubation of HRP-1 cells with 8-bromo-cAMP (a cAMP analog) and forskolin (an adenylyl cyclase activator) acutely stimulated the apical transport activity. This stimulation was further enhanced in the presence of IBMX (a phosphodiesterase inhibitor). Together these data show that the apical membrane of HRP-1 cells expresses an organic anion transport system that is regulated by cellular cAMP levels. This transport system appears to be different from the known taurocholate-transporting organic anion-transporting polypeptides and PAH-transporting organic anion transporters, both of which also mediate the transport of estrone sulfate and DHEAS.

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Characteristics of bile salt uptake into skate hepatocytes

Biochemical Journal ◽

10.1042/bj2990665 ◽

1994 ◽

Vol 299 (3) ◽

pp. 665-670 ◽

Cited By ~ 14

Author(s):

G Fricker ◽

V Dubost ◽

K Finsterwald ◽

J L Boyer

Keyword(s):

Substrate Specificity ◽

Bile Salt ◽

Transport System ◽

Bile Salts ◽

Organic Anion ◽

Anion Transport ◽

Organic Anion Transport ◽

Salt Uptake ◽

Anion Transport System ◽

Alpha 7

The substrate specificity for the transporter that mediates the hepatic uptake of organic anions in freshly isolated hepatocytes of the elasmobranch little skate (Raja erinacea) was determined for bile salts and bile alcohols. The Na(+)-independent transport system exhibits a substrate specificity, which is different from the specificity of Na(+)-dependent bile salt transport in mammals. Unconjugated and conjugated di- and tri-hydroxylated bile salts inhibit uptake of cholyltaurine and cholate competitively. Inhibition is significantly greater with unconjugated as opposed to glycine- or taurine-conjugated bile salts. However, the number of hydroxyl groups in the steroid moiety of the bile salts has only minor influences on the inhibition by the unconjugated bile salts. Since the transport system seems to represent an archaic organic-anion transport system, other anions, such as dicarboxylates, amino acids and sulphate, were also tested, but had no inhibitory effect on bile salt uptake. To clarify whether bile alcohols, the physiological solutes in skate bile, share this transport system, cholyltaurine transport was studied after addition of 5 beta-cholestane-3 beta,5 alpha,6 beta-triol, 5 alpha-cholestan-3 beta-ol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol. These bile alcohols inhibit cholyltaurine uptake non-competitively. In contrast, uptake of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol, which is Na(+)-independent, is not inhibited by cholyltaurine. The findings further characterize a Na(+)-independent organic-anion transport system in skate liver cells, which is not shared by bile alcohols and has preference for unconjugated lipophilic bile salts.

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ATP-dependent transport of beta-estradiol 17-(beta-D-glucuronide) in rat canalicular membrane vesicles

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1996.271.5.g791 ◽

1996 ◽

Vol 271 (5) ◽

pp. G791-G798

Author(s):

M. Vore ◽

T. Hoffman ◽

M. Gosland

Keyword(s):

Bile Acid ◽

Transport System ◽

Organic Anion ◽

Membrane Vesicles ◽

Anion Transport ◽

Organic Anion Transport ◽

Canalicular Membrane ◽

P Glycoprotein ◽

Anion Transport System ◽

Dependent Transport

The ATP-dependent transport of beta-estradiol 17-(beta-D-glucuronide) (E217G), a cholestatic metabolite of estradiol, was investigated in rat liver canalicular membrane vesicles. ATP-dependent transport was dependent on time and temperature and occurred into an osmotically sensitive space; kinetic analysis indicated a saturable transport system (Michaelis-Menten constant value, 75 microM; maximum transport rate, 598 pmol.min-1.mg protein-1). The steroid conjugates estradiol glucuronide, estriol 3-glucuronide, estriol 16 alpha-glucuronide, testosterone glucuronide, and the three-sulfate conjugate of 17G were effective inhibitors of transport. Bromosulfophthalein, S-(2,4-dinitrophenyl)glutathione, and glutathione disulfide, all substrates of the canalicular ATP-dependent non-bile acid organic anion transport system, were also effective inhibitors, whereas taurocholate had no effect on transport. Conversely, E217G inhibited the ATP-dependent transport of S-(2,4-dinitrophenyl)glutathione. Daunorubicin, vinblastine, etoposide, cyclosporin, and PSC-833, substrates/modulators of P-glycoprotein, were also potent inhibitors of E217G transport, and E217G competitively inhibited the ATP-dependent transport of daunorubicin. C219, a monoclonal antibody against P-glycoprotein, inhibited ATP-dependent transport of E217G and daunorubicin but not of taurocholate or S-(2,4-dinitrophenyl)glutathione. These data indicate that E217G is substrate of both the non-bile acid organic anion transport system and P-glycoprotein but not of the ATP-dependent bile acid transport system in canalicular membranes.

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A renal‐like organic anion transport system in the ciliary body epithelium of the eye (1064.16)

The FASEB Journal ◽

10.1096/fasebj.28.1_supplement.1064.16 ◽

2014 ◽

Vol 28 (S1) ◽

Author(s):

Jonghwa Lee ◽

Ryan Pelis

Keyword(s):

Transport System ◽

Ciliary Body ◽

Organic Anion ◽

Anion Transport ◽

Organic Anion Transport ◽

Anion Transport System ◽

Ciliary Body Epithelium

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A Renal-Like Organic Anion Transport System in the Ciliary Epithelium of the Bovine and Human Eye

Molecular Pharmacology ◽

10.1124/mol.114.096578 ◽

2015 ◽

Vol 87 (4) ◽

pp. 697-705 ◽

Cited By ~ 4

Author(s):

Jonghwa Lee ◽

Mohammad Shahidullah ◽

Adam Hotchkiss ◽

Miguel Coca-Prados ◽

Nicholas A. Delamere ◽

...

Keyword(s):

Transport System ◽

Organic Anion ◽

Anion Transport ◽

Ciliary Epithelium ◽

Organic Anion Transport ◽

Human Eye ◽

Anion Transport System

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ATP-dependent multispecific organic anion transport system in rat erythrocyte membrane vesicles

AJP Cell Physiology ◽

10.1152/ajpcell.1992.262.1.c104 ◽

1992 ◽

Vol 262 (1) ◽

pp. C104-C110 ◽

Cited By ~ 43

Author(s):

M. Heijn ◽

R. P. Oude Elferink ◽

P. L. Jansen

Keyword(s):

Bile Acids ◽

Transport System ◽

Organic Anion ◽

Membrane Vesicles ◽

Organic Anions ◽

Anion Transport ◽

Maximal Velocity ◽

Organic Anion Transport ◽

Anion Transporter ◽

Anion Transport System

The uptake of oxidized glutathione (GSSG) into inside-out membrane vesicles of Wistar rat erythrocytes was studied. Uptake was ATP dependent, into an osmotically active space, and saturable. Analysis of saturable ATP-dependent GSSG uptake showed two affinities for GSSG [concentration for half-maximal velocity (K1/2 1), 26 microM; K 1/2 2, 4 mM; maximum transport rate (Vmax 1), 100 pmol.mg-1.min-1; Vmax 2, 360 pmol.mg-1.min-1]. Interactions of the high-affinity system with different organic compounds were studied. Leukotriene C4, bromosulfophthalein-S-glutathione, and 2,4-dinitrophenyl-S-glutathione were effective inhibitors. In addition, anionic nonglutathione conjugates, like indocyanine green, rose bengal, dibromosulfophthalein, and sulfated or glucuronidated (divalent) bile acids inhibited GSSG transport. Monovalent bile acids had no influence on GSSG transport. Inhibition by 2,4-dinitrophenyl-S-glutathione [inhibition constant (Ki) = 2.6 microM] and sulfated glycolithocholic acid (Ki = 2.9 microM) was purely competitive. The use of adenosinetriphosphatase (ATPase) inhibitors suggested a resemblance with E1E2-type ATPase. Vesicles of erythrocytes isolated from the TR- rat, a mutant rat strain with a defective biliary secretion of organic anions, have an impaired uptake of GSSG (Vmax was decreased 2-fold). In conclusion, erythrocytes have an ATP-dependent organic anion transport system that can be inhibited by a broad range of organic anions. This system is very similar if not identical to the hepatocanalicular ATP-dependent organic anion transporter.

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