UPTAKE OF TAUROCHOLIC ACID AND CHOLIC-ACID IN ISOLATED HEPATOCYTES FROM RAINBOW-TROUT

The uptake of the bile acids cholate (CHA) and taurocholate (TCHA) was studied in isolated hepatocytes from rainbow trout (Oncorhynchus myki ss). Both CHA and TCHA were taken up in a concentration- and temperatu re-dependent manner with optimum temperature at 15 degrees C and a str ikingly efficient uptake even at low temperatures (0-5 degrees C). The total uptake was a combination of a saturable [Michaelis-Menten const ant (K-m) for CHA, 20 mu M; K-m for TCHA, 19 mu M] and a nonsaturable component. The maximal uptake rate of the saturable component was 416 and 805 pmol.mg protein(-1).min(-1) for CHA and TCHA, respectively. Th e uptake of both bile acids was shown to be energy dependent, since it was inhibited by the metabolic inhibitors antimycin A, oligomycin and carbonyl cyanide m-chlorophenylhydrazone. The uptake was clearly Naindependent, since isosmotic replacement of extracellular Na+ by Li+, choline, or K+ did not inhibit the uptake. Furthermore, it seemed to b e independent of the presence of extracellular Cl-, since it was not i nhibited by replacement of Cl- with sodium gluconate. On the whole, ou r results show that the hepatocellular uptake of bile acids in rainbow trout is mediated by a Na+-independent carrier system, with character istics resembling the corresponding transport component in mammalian h epatocytes, but with high efficiency even at low temperatures.