Immunologic distribution of an organic anion transport protein in rat liver and kidney

Abstract

A Na(+)-independent organic anion transport protein was recently cloned from rat liver using a Xenopus laevis oocyte expression system [E. Jacquemin, B. Hagenbuch, B. Stieger, A.W. Wolkoff, and P.J. Meier, Proc. Natl. Acad. Sci. USA 91: 133-137, 1994]. Although expression of this protein is sufficient for cells to transport the organic anion bromosulfophthalein, little is known about its cell biology or biochemical characteristics. Northern blot analysis performed under high-stringency conditions revealed hybridization with RNA only from liver and kidney; transcripts appeared the same in these two organs. Within kidney, hybridization was greatest when RNA extracted from the outer medulla was used. Immunoblot analysis revealed that in liver, the transporter was enriched in 0.1 M Na2CO3-extracted membranes and sinusoidal plasma membrane preparations, consistent with its being an integral membrane protein. This 80-kDa protein migrated as a 65-kDa protein after treatment with N-glycanase. Immunomorphological examination of liver revealed basolateral plasma membrane localization. In 0.1 M Na2CO3-extracted membranes of kidney, the transporter migrated as an 83-kDa protein on nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On reduction, it resolved into peptides of 33 and 37 kDa. SDS-PAGE migration of the liver protein was unaffected by reduction. Immunomorphological examination of kidney revealed apical plasma membrane localization in the S3 segment of the proximal tubule of the outer medulla. Differential processing and trafficking of this transporter in liver and kidney may have important functional and regulatory consequences.

Systemic gut microbial modulation of bile acid metabolism in host tissue compartments

“…Additionally, it is known that the hepatic extraction of free bile acids is also less efficient compared with the conjugated forms (35), and this further explains the greater proportion of unconjugated bile acids in the systemic circulation and consequently, the kidney and heart. At physiological pH, conjugated bile acids are negatively charged and require carrier-mediated transport across tissue membranes; therefore, it is likely that these organspecific profiles arise from selective uptake caused by differential expression of bile acid transporters in the renal tubular cells and cardiomyocytes (28)(29)(30)(31)(32). In a previous study, Dupont et al (36) showed organ-specific differences in the ratios of glycine-and taurine-conjugated bile acids in a range of tissues from miniature swine using gas liquid chromatography.…”

“…The global signaling capacity of bile acids is currently unclear; however, the expression of bile acid receptors FXR and TGR5 in tissues outside of the enterohepatic circulation, including the kidney (25) and heart (26,27), suggests a greater role throughout the body. Expression of bile acid transporters in renal tubular cells [Asbt (28), organic anion transporting polypeptide 1 (OATP1) (29), and kidney specific organic anion transporter (OATK2) (30)] and cardiomyocytes (31,32) further supports this proposition. Moreover, the involvement of bile acids in the regulation of glucose homeostasis is consistent with the expression of FXR in pancreatic β-cells, which has been shown to play an essential role in the regulation of insulin transcription and secretion induced by glucose (33).…”

Rat Organic Anion Transporter 3 and Organic Anion Transporting Polypeptide 1 Mediate Perfluorooctanoic Acid Transport

“…The renal level of oatp1 mRNA was altered by changing sexhormonal states. 9) Considering that oatp1 is expressed in the brush border membrane of renal proximal tubules 20) and is responsible for reabsorption of several drugs, 21) oatp1 is a candidate PFOA transporter. Expression of oatp1 in the cells significantly increased the uptake of both [ 3 H]-taurocholate, a known substrate for oatp1, and [ 14 C]-PFOA (Fig.…”

Molecular cloning and functional characterization of the mouse organic-anion-transporting polypeptide 1 (Oatp1) and mapping of the gene to chromosome X

“…All these members of the Oatp gene family are found in many different tissues besides the ones they were cloned from. Oatp1 is expressed, in addition to the sinusoidal membrane of hepatocytes [9], in the apical membrane of the proximal tubule [10] and in the apical membrane of the choroid plexus [11]. Oatp2 protein was detected in rat liver hepatocytes, endothelial cells of the blood\brain barrier [12][13][14] and the choroid plexus [12].…”