Regulation of taurocholate transport in freshly isolated proximal tubular cells of the rat kidney by protein kinases.
OBJECTIVE
The bile acids filtered through the glomeruli nearly completely escape urinary excretion due to an efficient tubular reabsorption process. Reabsorption is mediated mainly by the sodium-dependent bile acid transporter (ASBT) which is located in the brush border membranes of proximal tubular cells. The present study addresses the question whether this transporter is subject to short-term regulation by protein kinases.


METHODS
The effects of specific activators or inhibitors of eight different protein kinases (PKs) on 3H-taurocholate uptake of proximal tubular cells were investigated. The cells were freshly isolated from rat kidneys by nycodenz density gradient centrifugation.


RESULTS
Activation of the cAMP/PKA system by forskolin, 8-Br-cAMP, or the cAMP phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine significantly diminished cellular 3H-taurocholate uptake whereas 8-Br-cGMP had no effect. Also the MEK1/2 inhibitors PD98059 and U0126, and the p38 mitogen-activated protein (MAP) kinase inhibitor SB203580 decreased 3H-taurocholate uptake. Phorbol myristate acetate and dioctanolglycerol, activators of PKC, and chelerythrine, a selective inhibitor of PKC, did not affect 3H-taurocholate uptake. Likewise the phosphatidylinositol-3 kinase inhibitor wortmannin and the tyrosine kinase inhibitor genistein induced no significant change of cellular 3H-taurocholate uptake. In a sodium-free medium forskolin and PD98059 did not affect 3H-taurocholate uptake but SB203580 significantly decreased it.


CONCLUSIONS
It is concluded that PKA and MAP kinases are involved in the regulation of the ASBT-mediated taurocholate uptake into proximal tubular cells. p38 MAP kinase may have an additional effect on a sodium-independent tubular taurocholate transporter.
Schlattjan
Jan Henrik
JH
Department of Pharmacology and Toxicology, Aachen University, Aachen, Germany.
Benger
Susanne
S
Herrler
Andreas
A
von Rango
Ulrike
U
Greven
Joachim
J
D000818:Animals; D001693:Biological Transport, Active; D002478:Cells, Cultured; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D013656:Taurocholic Acid / Q000493:pharmacokinetics*
D013656:Taurocholic Acid; D011494:Protein Kinases