Amphibian hepatocytes have been prepared in both high yield and purity using a collagenase perfusion technique. The isolated cells attach efficiently in serum-free medium to collagen-coated culture dishes and subsequently form monolayers. These cultures can be maintained in an appropriate medium for over one week with minimal cell loss. The nuclear labelling index of cells exposed to [3H]thymidine indicates a very low level of cell growth. Twenty-four hour exposure to dexamethasone induces tyrosine aminotransferase activity throughout the culture period. Monolayers incorporate [3H]leucine linearly into acid-insoluble material with approx. 40% of all synthesis devoted to secreted protein. Polyacrylamide gel electrophoresis of proteins in the presence of sodium dodecyl sulfate shows the majority of proteins present in whole serum are synthesized and secreted by the cultured hepatocytes. The absolute rate of protein secretion on the first day of culture is approx. 73 μg/day/mg cell protein which subsequently declines and plateaus at 30% of this level by the 4th-5th day of culture. However, when hepatocytes are cultured in the continued presence of insulin, the drop in protein secretion is completely inhibited. Cultures of hepatocytes isolated from female frogs and subsequently exposed to 17-B estradiol in culture, synthesize and secrete the egg-yolk protein precursor vitellogenin. The protein initially appears as a minor component in the medium 1-2 days after hormone addition. Its rate of synthesis, relative to other secreted proteins, increases with time so that it ultimately constitutes the majority of protein being exported after 6 days of treatment. Parallel with vitellogenin induction is an increase in rate of total protein secretion reaching a 2-fold increase at maximal stimulation. The results show that viable, monolayer cultures of amphibian hepatocytes can be prepared which retain the ability to respond directly to added estrogen by synthesizing vitellogenin.
ASJC Scopus subject areas
- Cell Biology