The role of sodium in the uptake of ursodeoxycholic acid in isolated hamster hepatocytes.
The uptake of ursodeoxycholic acid (UDCA) was studied in isolated hamster hepatocytes. The uptake was rapid and linear up to 60 seconds for each concentration studied. When the uptake rate was plotted against UDCA concentration, the curve was nonlinear, indicating both saturable and nonsaturable uptake mechanisms. The nonsaturable process had a diffusion constant of 0.01 nmol.s-1.g of cell.mumol/L-1. The saturable component was characterized by a maximum rate of uptake (Vmax) of 5.68 nmol.s-1.g of cell-1 and a Michaelis constant (Km) of 224 mumol/L. In the presence of monensin, ouabain, and amiloride, the uptake of UDCA was significantly decreased by 35% to 55%, whereas the sodium-independent uptake of UDCA was not affected by either monensin or amiloride, thereby confirming sodium dependence of UDCA uptake. The sodium-dependent uptake of UDCA was characterized by a Vmax and a Km of 1.57 nmol.s-1.g of cell-1 and 46 mumol/L, respectively. The rate of uptake of UDCA was maximal at extracellular sodium concentrations > or = 20 mmol/L. Furthermore, the uptake of UDCA was competitively inhibited by both taurocholic acid and cholic acid with an inhibitory constant (Ki) of 60 mumol/L and 48 mumol/L, respectively. Finally, 1 mmol/L of 4,4'-diisothiocyano-2,2'-disulfonic stilbene (DIDS) inhibited solely the sodium-dependent uptake of cholic acid and UDCA. These findings confirm that the hepatocellular uptake of UDCA involves, at least in part, a sodium-dependent, ouabain, amiloride, and DIDS-sensitive transporter.
Bouscarel
B
B
Department of Medicine, George Washington University Medical Center, Washington, DC 20037.
Nussbaum
R
R
Dubner
H
H
Fromm
H
H
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000818:Animals; D001647:Bile Acids and Salts / Q000494:pharmacology; D002469:Cell Separation; D019826:Cholic Acid; D002793:Cholic Acids / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics; D002794:Choline / Q000494:pharmacology; D006224:Cricetinae; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008647:Mesocricetus; D012964:Sodium / Q000037:antagonists & inhibitors / Q000502:physiology*; D014580:Ursodeoxycholic Acid / Q000037:antagonists & inhibitors / Q000493:pharmacokinetics*
D001647:Bile Acids and Salts; D002793:Cholic Acids; D014580:Ursodeoxycholic Acid; D012964:Sodium; D019826:Cholic Acid; D002794:Choline; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid