Short-term feedback regulation of bile salt uptake by bile salts in rodent liver.
The sodium taurocholate cotransporting polypeptide (Ntcp) is the major bile salt uptake transporter at the sinusoidal membrane of hepatocytes. Short-term feedback regulation of Ntcp by primary bile salts has not yet been investigated in vivo. Subcellular localization of Ntcp was analyzed in Ntcp-transfected HepG2-cells by flow cytometry and in immunofluorescence images from tissue sections by a new automated image analysis method. Net bile salt uptake was investigated in perfused rat liver by a pulse chase technique. In Flag-Ntcp-EGFP (enhanced green fluorescent protein) expressing HepG2-cells, taurochenodeoxycholate (TCDC), but not taurocholate (TC), induced endocytosis of Ntcp. TCDC, but not TC, caused significant internalization of Ntcp in perfused rat livers, as shown by an increase in intracellular Ntcp immunoreactivity, whereas Bsep distribution remained unchanged. These results correlate with functional studies. Rat livers were continuously perfused with 100 μmol/L of TC. 25 μmol/L of TCDC, taurodeoxycholate (TDC), tauroursodeoxycholate (TUDC), or TC were added for 30 minutes, washed out, followed by a pulse of (3) [H]-TC. TCDC, but not TDC, TUDC, or TC significantly increased the amount of (3) [H]-TC in the effluent, indicating a reduced sinusoidal net TC uptake. This effect was sensitive to chelerythrine (protein kinase C inhibitor) and cypermethrin (protein phosphatase 2B inhibitor). Phosphoinositide 3-kinase (PI3K) inhibitors had an additive effect, whereas Erk1/2 (extracellular signal activated kinase 1/2), p38MAPK, protein phosphatase 1/2A (PP1/2A), and reactive oxygen species (ROS) were not involved.


CONCLUSIONS
TCDC regulates bile salt transport at the sinusoidal membrane by protein kinase C- and protein phosphatase 2B-mediated retrieval of Ntcp from the plasma membrane. During increased portal bile salt load this mechanism may adjust bile salt uptake along the acinus and protect periportal hepatocytes from harmful bile salt concentrations.
Department of Gastroenterology, Hepatology and Infectious Diseases, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany.
Stefanie
S
Mühlfeld
Olga
O
Domanova
Thomas
T
Berlage
Claudia
C
Stross
Angelika
A
Helmer
Verena
V
Keitel
Dieter
D
Häussinger
Ralf
R
Kubitz
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D053119:Benzophenanthridines / Q000494:pharmacology; D001647:Bile Acids and Salts / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D002756:Cholagogues and Choleretics / Q000378:metabolism* / Q000494:pharmacology; D015536:Down-Regulation; D004705:Endocytosis; D025461:Feedback, Physiological; D056945:Hep G2 Cells; D006801:Humans; D008099:Liver / Q000378:metabolism*; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011722:Pyrethrins / Q000494:pharmacology; D051381:Rats; D027981:Symporters / Q000378:metabolism*; D013655:Taurochenodeoxycholic Acid / Q000378:metabolism* / Q000494:pharmacology; D013656:Taurocholic Acid / Q000378:metabolism / Q000494:pharmacology; D013657:Taurodeoxycholic Acid / Q000494:pharmacology
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D053119:Benzophenanthridines; D001647:Bile Acids and Salts; D065095:Calcineurin Inhibitors; D002756:Cholagogues and Choleretics; D029363:Organic Anion Transporters, Sodium-Dependent; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D011722:Pyrethrins; D027981:Symporters; D013655:Taurochenodeoxycholic Acid; D013656:Taurocholic Acid; D013657:Taurodeoxycholic Acid; C490548:Abcb11 protein, rat; C071908:sodium-bile acid cotransporter; C017160:cypermethrin; C031655:ursodoxicoltaurine; C016299:chelerythrine