Mechanism of inhibition of hepatic bile acid uptake by amiloride and 4,4'-diisothiocyano-2,2'-disulfonic stilbene (DIDS).
The mechanisms by which amiloride and 4,4'-diisothiocyano-2,2'-disulfonic stilbene (DIDS) inhibit hepatic uptake of cholate and taurocholate (TC) were investigated in isolated rat hepatocytes. Amiloride inhibited Na(+)-dependent uptake of cholate and TC only when hepatocytes were preincubated with amiloride, indicating an indirect effect of amiloride. Time-dependent studies showed that the inhibition of bile acid uptake was associated with a parallel increase in intracellular Na+ concentration ([Na+]i). Although amiloride decreased intracellular pH, this decrease preceded amiloride-induced inhibition of bile acid uptake and increase in [Na+]i. Amiloride inhibited bile acid uptake, decreased membrane potential, and increased [Na+]i with comparable concentration dependency. DIDS inhibited Na(+)-dependent uptake of cholate and TC non-competitively. Neither DIDS nor amiloride inhibited Na(+)-independent uptake of cholate and TC. These results indicate that amiloride inhibits Na(+)-dependent cholate and TC uptake by decreasing the transmembrane Na(+)-gradient, and further support the hypothesis that two different transporters may be involved in hepatic bile acid uptake by Na(+)-dependent and Na(+)-independent mechanisms.
Anwer
M S
MS
Department of Medicine, Tufts University School of Veterinary Medicine, North Grafton, MA 01536.
Branson
A U
AU
Atkinson
J M
JM
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology; D001647:Bile Acids and Salts / Q000378:metabolism*; D002478:Cells, Cultured / Q000187:drug effects; D019826:Cholic Acid; D002793:Cholic Acids / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000032:analysis / Q000494:pharmacology; D013656:Taurocholic Acid / Q000378:metabolism
D001639:Bicarbonates; D001647:Bile Acids and Salts; D002793:Cholic Acids; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D013656:Taurocholic Acid; D000584:Amiloride; D012964:Sodium; D019826:Cholic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid