The protein synthesizing capacity of liver parenchymal cells isolated from 3-, 12-, 24-, 31- and 36-month-old rats was determined by the incorporation of 14C-leucine. Conditions for optimum protein synthesis included the use of an enriched medium (modified Waymouth's MB 752/1) and cell suspension concentrations ranging from 0.25 to 4 × 106 cells/ml medium. The cells were incubated with a dose of 6 μmol leucine/ml medium for 2 h at 37°C under an atmosphere of 95% O2 and 5% CO2. With parenchymal cells isolated from 3-month-old rats, a leucine incorporation rate of 14.4 nmol leucine/h/106 cells was found. The capacity of the parenchymal cells to synthesize protein decreased between 3 and 12 months, remained constant between 12 and 24 months and increased between 24 and 36 months. Degradation of newly synthesized proteins or reutilization of 14C-leucine did not occur during the incubation period.

The specific liver function of removing foreign compounds from the serum was investigated by measuring the uptake of |35S| bromsulfophthalein by isolated liver parenchymal cells. To obtain a maximum uptake, the parenchymal cells in cell concentrations ranging between 0.05 and 0.4 × 106 cells/ml were incubated with a dose of 30 nmoles |35S| bromsulfophthalein/ml for 15 min at 37°C. An uptake of 2.87 ± 0.18 nmoles bromsulfopthalein/106 cells was measured. The saturation of the rate of bromsulfophthalein uptake with increasing amounts of bromsulfophthalein in the medium, the ability to take up free bromsulfopthalein against a concentration gradient and the dependence of the uptake mechanism on temperature and metabolic energy suggest the presence of an active carrier system for the uptake of bromsulfophthalein by liver parenchymal cells.

Viable isolated parenchymal cells were incubated in a modified Waymouth medium under an oxygen tension of 30×103 Pa at pH 7.8. Under these conditions, hepatocytes from 3-month-old rats synthesized 5.8 μg albumin/h/106 cells. This value nearly equals the synthesizing capacity of intact liver tissue and is the highest activity reported so far for isolated hepatocytes. Parenchymal cells isolated from 36-month-old rats synthesized more albumin as compared to cells from 3-month-old rats. The albumin synthesizing capacity of cells isolated from 12-month-old rats was less than that of cells from 3-month-old rats.