Cholic acid uptake and isolated rat hepatocytes.
Cholic acid uptake was studied in isolated rat hepatocytes using a centrifugal filtration technique to allow rapid sampling. Hepatocytes were found to adsorb as well as to transport cholic acid. The adsorption was characterized by a capacity of 24 nmol X mg cell protein-1 and an association constant of 0.59 X 103 M-1. Cholic acid uptake was linear with respect to concentration at or below 10 degree C, suggesting a unsaturable uptake process which was considered to represent simple diffusion and is quantitated by a diffusion coefficient of 1.76 pmol cholic acid X min-1 X mg protein-1 X muM-1. Above 10 degrees C the uptake curve was biphasic. After subtracting the unsaturable component from uptake rates at higher temperatures, a curve showing saturable kinetics resulted. The apparent Km and V values at 37 degrees C were calculated to be 31muM and 0.8 nmol X min-1 X mg protein-1 respectively. This saturable uptake process was temperature-dependent with an activation energy of 13 kcal X mol-1 (5.44 X 104 J X mol-1) and was inhibited by oligomycin and KCN. Countertransport was demonstrated with cholic, taurocholic and chenodeoxycholic acids. The results suggest that cholic acid is transported by an energy-dependent carrier-mediated process in addition to simple diffusion by hepatocytes, and that the postulated carrier has affinity for other bile acids.
D000327:Adsorption; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002793:Cholic Acids / Q000378:metabolism*; D003486:Cyanides / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D009840:Oligomycins / Q000494:pharmacology; D051381:Rats; D013696:Temperature
D002793:Cholic Acids; D003486:Cyanides; D009840:Oligomycins