Analysis of discontinuous variation in albumin production by hepatoma cells at the cellular level

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Abstract
The clonal variation in the rate of albumin production in cultured rat hepatoma cells has been studied on a cellular basis by immunoperoxidase techniques using specific antisera against rat serum albumin. Previously, it has been shown that an array of clonal hepatoma cell populations that produce serum albumin at different rates can be isolated simply by subcloning a single clonal hepatoma cell line (Fu5). The present study demonstrates conclusively that this phenotypic variation is the result of quantal shifts in the rate of albumin production in the individual cells and is not due to changes in the percentage of albumin-producing cells. Also, by analyzing individual colonies as they develop from single cells, it was possible to establish that the rate of variation in albumin content in several hepatoma cell clones is on the order of 0.5–1.4 10−2 per cell per generation. This variation in albumin content probably reflects shifts in the rate of albumin synthesis. Even after several sequential subclonings, the same clonal variation persists. The variants are not the result of fluctuations in albumin synthesis with different phases of the cell cycle.