Characteristics of cholic acid uptake in primary cultured hepatocytes

The characteristics of cholic acid uptake by primary cultured hepatocytes was studied. The cholic acid uptake below 10 degrees C was unsaturable, while that determined at 20 degrees and 37 degrees C showed a biphasic type, which suggested the presence of a saturable process. This saturable process was a temperature-dependent and carrier-mediated transport process with an activation energy of 36.1 Kcal/mol. The apparent Km and Vmax values at 37 degrees C were 57.1 microM and 0.566 nmoles/mg protein/min, respectively. The saturable process was inhibited by 2,4-dinitrophenol and ouabain, and reduced significantly in the absence of sodium, suggesting that this process is energy- and sodium-dependent. The cholic acid uptake mediated by the saturable process in the absence of sodium was, however, significantly larger than that mediated by the unsaturable process. These results suggest that the transport of cholic acid in primary cultured hepatocytes may consist of three different types: unsaturable, sodium and energy-dependent carrier-mediated, and sodium-independent and energy-dependent processes, respectively. The presence of a common transport carrier for cholic acid and its conjugates with taurine and glycine in primary cultured hepatocytes was also suggested.