Morphological and biochemical observations on mammalian liver cells in culture. Isolation of a clonal strain from rat liver

Repeated establishment of diploid epithelial cell cultures from normal and partially hepatectomized rats

A number of liver epithelial cell cultures were established from 10 to 12-d-old sucklings, 6 to 8-wk-old young adults, or from 2 to 18-month-old partially hepatectomized rats. Improvements in the methods for cell isolation and culture yielded replicating cells from every experiment and they were maintained for different periods with regular passages. The proliferative potential in vitro of adult rat liver cells could be increased if the rats were subjected to partial hepatectomy before cell isolation. In the early passages, the majority of the cells were found to have a true diploid karyotype as studied by the Giemsa-banding technique. Under the culture conditions described, a very high percentage of cells remained in the diploid range for, in most cases, at least 4 months and in some cases for up to 6 months. Afterward, the karyotype was unstable, but no "crisis" period was seen before the cells became aneuploid. Until this time, the growth characteristics of the cells also followed a normal pattern showing density dependent inhibition of division and a lack of markers associated with malignancy. The cultured liver cells exhibited a number of liver specific properties when they were maintained as a confluent monolayer. The early passages of diploid epithelial cell cultures derived from normal and regenerating rat liver are good models for studies of the regulation of cell division and the changes that are related to carcinogenesis.

Cell types in long-term propagable cultures of rat liver

Under the conditions of this experiment, propagable hepatic epithelial cells in long-term culture were derived from a small, nonparenchymal precursor cell present in the liver in vivo. Progeny of the nonparenchymal precursor cell weakly expressed some hepatocyte-like properties in culture. Hepatocytes were not clonogenic under the conditions of this experiment. Propagable hepatic epithelial cells in long-term culture probably originate from hepatic stem cells in vivo. Terminal biliary ductular cells are facultative stem cells for hepatocytes.

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.

Hormonal regulation of amino acid transport and gluconeogenesis in primary cultures of adult rat liver parenchymal cells

Amino acid transport was studied in primary cultures of parenchymal cells isolated from adult rat liver by a collagenase perfusion technique and maintained as a monolayer in a serum-free culture medium. These cells carried out gluconeogenesis from three carbon precursors (alanine, pyruvate, and lactate) in response to glucagon addition. Amino acid transport was assayed by measuring the uptake of the nonmetabolizable amino acid, alpha-aminoisobutyric acid (AIB). Addition of insulin or glucagon to culture rat liver parenchymal cells resulted in an increased influx of AIB transport. The glucocorticoid, dexamethasone, when added alone to cultures did not affect AIB transport. However, prior or simultaneous addition of dexamethasone to glucagon-treated cells caused a strong potentiation of the glucagon induction of AIB transport. Kinetic analysis of the effects of insulin and glucagon demonstrated that insulin increased the Vmax for transport without changing the Km while glucagon primarily decreased the Km for AIB transport. The effect of dexamethasone was to increase the Vmax of the low Km system.

Modification of pyruvate kinase isozymes in prolonged primary cultures of adult rat hepatocytes

Pyruvate kinase isozymic changes were studied in the adult hepatocyte cultures, by electrophoretic, kinetic and immunological methods. We were able to maintain parenchymal cells from normal adult rat liver in non-proliferating monolayer cultures up to 10 days. Hepatocytes appeared to contain a dominant PK I type up to 4-5 days of culture. After day 5, PK III type was regularly present with PK I and after 7 days PK III type was always the only isozyme detected in culture. It must be pointed out that, by the Ouchterlony method and sometimes by electrophoresis, concentrated extracts from freshly isolated hepatocytes or starting hepatocyte cultures did also contain Pyruvate kinase PK III type. These results suggest that Pyruvate kinase III is present but partly repressed in the adult parenchymal cells and becomes derepressed in culture.