title: Role of chloride and intracellular pH on the activity of the rat hepatocyte organic anion transporter.
abstract: Previous studies in cultured rat hepatocytes revealed that initial uptake of sulfobromophthalein (BSP) was markedly reduced upon removal of Cl- from the medium. In the present study, unidirectional Cl- gradients were established in short-term cultured rat hepatocytes and their effect on BSP uptake was determined. These investigations revealed that BSP uptake requires external Cl- and is not stimulated by unidirectional Cl- gradients, suggesting that BSP transport is not coupled to Cl- transport. In contrast, BSP transport is stimulated by an inside-to-outside OH- gradient, consistent with OH- exchange or H+ cotransport. As the presence of Cl- is essential for but not directly coupled to BSP transport, binding of 35S-BSP to hepatocytes was determined at 4 degrees C. This revealed an approximately 10-fold higher affinity of cells for BSP in the presence as compared to the absence of Cl- (Ka = 3.2 +/- 0.8 vs. 0.42 +/- 0.09 microM-1; P less than 0.02). Affinity of BSP for albumin was Cl(-)-independent, and was approximately 10% of its affinity for cells in the presence of Cl-. These results indicate that extracellular Cl- modulates the affinity of BSP for its hepatocyte transporter.
authors.affiliation: Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: A D
authors.initials: AD
authors.lastname: Min
authors.forename: K L
authors.initials: KL
authors.lastname: Johansen
authors.forename: C G
authors.initials: CG
authors.lastname: Campbell
authors.forename: A W
authors.initials: AW
authors.lastname: Wolkoff
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000378:metabolism*; D008297:Male; D011485:Protein Binding; D051381:Rats; D011919:Rats, Inbred Strains; D012710:Serum Albumin, Bovine / Q000378:metabolism; D013448:Sulfobromophthalein / Q000493:pharmacokinetics
chemical_list: D027321:Anion Transport Proteins; D002352:Carrier Proteins; D002712:Chlorides; D013448:Sulfobromophthalein; D012710:Serum Albumin, Bovine