Some morphological and biochemical characteristics of isolated rat liver cells dissociated with sodium tetraphenylboron and cultured in suspension

Hepatocyte suspensions and cultures as tools in experimental carcinogenesis

Isolation of preneoplastic cell populations would greatly facilitate analysis of the development of liver carcinogenesis. Suspensions of intact single cells can be prepared in an almost quantitative yield by two-step perfusion of the isolated liver. In the first step the liver is perfused with a Ca2+-free buffer (or with EGTA) in order to irreversibly cleave the desmosomes; in the second step perfusion with Ca2+-activated collagenase dissolves the collagenous extracellular matrix. The resulting single-cell suspension will be a mixture of intact normal and preneoplastic hepatocytes, other liver cell types (mostly Kupffer and endothelial cells), damaged cells, and subcellular debris. Intact hepatocytes can be purified--e.g., by differential centrifugation--but separation of preneoplastic from normal cells has not yet been achieved. Density gradient separation or selection in culture on the basis of the unique properties of preneoplastic hepatocytes (e.g., drug resistance) may prove useful. The use of hepatocyte cultures and liver-derived epithelial cell lines as test systems and models for chemical carcinogenesis in vitro is briefly reviewed.

Isolation and preliminary characterization of rat liver cells resistant to 7-ketocholesterol

Two clones of the rat liver cell line, GAI, were selected and propagated in 4 microgram/ml of the cholesterol analogue, 7-ketocholesterol. One of the variants was also found to be resistant to another toxic analogue, 25-hydroxycholesterol. 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) activity was elevated in both variant clones, but was not increased substantially upon incubation of the cells in lipid-depleted medium. The reductase activity was increased 3-fold in the wild type cells under the same conditions. Incubation of the cells in lipid-depleted medium resulted in a 3-fold increase in the rate of sterol synthesis from [14C]acetate in all three types. In the presence of 2 microgram/ml 7-ketocholesterol, the reductase activity in all three cell lines decreased at an equal rate, but activity of the enzyme was still measurable after 48 h in the presence of the analogue. Sterol synthesis was reduced almost to zero in the wild type cells under these conditions, while the variant cells retained 12--15% of their capacity for sterol synthesis. These results are interpreted to indicate that 7-ketocholesterol, besides affecting sterol synthesis at the level to 3-hydroxy-3-methylglutaryl coenzyme A reductase, must also affect sterol synthesis at another step further along the synthetic pathway.

Epithelial rat liver cells have cell surface receptors recognizing a phosphorylated carbohydrate on lysosomal enzymes

Receptor-mediated endocytosis of alpha-N-acetylglucosaminidase by cultured epithelial rat liver cells is inhibited by mannose, L-fucose and most effectively by mannose 6-phosphate. Endocytosis of alpha-N-acetylglucosaminidase is lost after treatment of the enzyme with alkaline phosphatase. These findings indicate that epithelial rat liver cells possess cell surface receptors that recognize a phosphorylated carbohydrate on alpha-N-acetylglucosaminidase, as was previously reported for cell surface receptors of human skin fibroblasts. Inhibition of alpha-mannosidase endocytosis by epithelial rat liver cells in the presence of mannose 6-phosphate and loss of enzyme endocytosis after treatment with alkaline phosphatase suggest that this enzyme is recognized by the same receptor.

Changes in size, DNA content, and nuclear ploidy of rat liver produced by the environmental microflora

Effects of the environment microflora on rat liver were studied in the present investigation. Rats born under sterile conditions were bred either in a germfree or in a "SPF" environment. At 12 weeks of age the liver of the SPF rats was larger by 20% and contained more DNA than germfree rat liver. Volume analysis, by means of a particle counter, of isolated nuclei suggested that the increase of DNA was due to an increase of hepatic nuclear ploidy. The findings show that infections may influence liver size and ploidy. They indicate that the state of infection should be controlled in animal studies which concern the regulation of liver growth and ploidy or which use liver weight and DNA as reference standards.

Improved isolation, separation and cytochemistry of living cells

1. This paper describes improved methods of obtaining, purifying and studying bulk suspensions of isolated living hepatocytes and other cells of adult rats and urodeles. 2. The cells were isolated largely by dissolving the hepatic ground substance through the extracorporeal portal perfusion and further incubation of the excised liver with 0.05% collagenase and 0.1% hyaluronidase. The different kinds of cells were then separated from one another by counter-current centrifugation. The isolated cells were examined by differential interference, phase-contrast, amplitude-contrast, ultraviolet, fluorescence and electron microscopy. Various cytochemical tests were carried out. Whenever possible, for each method of examination, the isolated cells were compared with cells of the same kind which had not undergone isolation. 3. Dye-exclusion, lysochromy, fluorescence and differential interference microscopical analysis indicated viability rates between 75 and 99%. Succinate dehydrogenase activity was preserved at a high level in nearly all isolated cells. In hepatocytes, the essentially extracellular cells. In hepatocytes, the essentially extracellular 'soluble' alkaline phosphatase activity of bile canaliculi was retained. Living hepatocytes were studied by super-modulating methods of microscopy for the first time, with somewhat unexpected findings. It now seems probable that previous methods of tissue preparation produced gross alterations in hepatocyte mitochondria. The assessment of the viability of isolated cells was re-examined. 4. The methods described may permit a more meaningful correlation between biochemical, cytochemical, ultrastructural and biophysical findings than that obtainable by the use of current methods.

Tyrosine transaminase induction by dexamethasone in a new rat liver cell line

A cell line derived from normal, adult rat liver has been established; the cells are similar to hepatocytes, as shown by electron microscopy. The addition of dexamethasone to the culture medium induced a three- to sixfold increase in the specific activity of tyrosine alpha-ketoglutarate transaminase; this increase was inhibited by the simultaneous addition of cycloheximide or actinomycin D. The latter, when added to cells given prior treatment with dexamethasone, further enhanced the transaminase activity. Contact-inhibited cells showed a lower response to dexamethasone than exponentially growing cells.