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Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver

Frei, Pascal and Gao, Bo and Hagenbuch, Bruno and Mate, Alfonso and Biber, Jürg and Murer, Heini and Meier, Peter J. and Stieger, Bruno. (2005) Identification and localization of sodium-phosphate cotransporters in hepatocytes and cholangiocytes of rat liver. American journal of physiology. Gastrointestinal and liver physiology, Vol. 288, H. 4 , G771-G778.

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Official URL: http://edoc.unibas.ch/dok/A5261594

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Abstract

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.
Faculties and Departments:11 Rektorat und Verwaltung > Vizerektorat Forschung
UniBasel Contributors:Meier-Abt, Peter J.
Item Type:Article, refereed
Bibsysno:Link to catalogue
Publisher:American Physiological Society
ISSN:0002-9513
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:22 Mar 2012 14:21
Deposited On:22 Mar 2012 13:23

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