The alkaline phosphatase content of different tissue culture cell lines has been shown to vary from no detectable activity to high enzyme concentration. Within the epithelial lines studied alkaline phosphatase is either constitutive or inducible. Two epithelial cell strains in which alkaline phosphatase was "absent" could be induced to develop significant amounts of the enzyme when grown in the presence of Al-hydrocortisone. Phosphate did not repress enzyme induction by prednisolone. Under conditions of deadaptation the induced enzyme was diluted by cell multiplication. The mouse fibroblastic L line and several human fibroblastic lines did not contain alkaline phosphatase when grown under the conditions described nor could they be induced to produce the enzyme when cultivated in medium with prednisolone.A1-Hydrocortisone has other characteristic effects on established mammalian cell cultures which vary among cell lines. Human epithelial lines show reduction in cell multiplication with increase in mitotic index. The cytoplasm is increased and cell volume is nearly doubled. Mouse fibroblasts show a similar reduction in cell multiplication with a decrease in mitotic index. There is no increase in cell cytoplasm. Human fibroblast strains show no inhibition of multiplication or alteration in total cell protein when grown in medium containing prednisolone.Antisera prepared against "negative" prednisolone-inducible human cell lines and against a positive human line inhibited alkaline phosphatase activity to an equal degree.
I N T R O D U C T I O NMost h u m a n cells capable of continuous cultivation in vitro have been found to be similar in their nutritional requirements (1), immunologic reactivity (2), and virus susceptibility (3). T h e e n z y m e composition of four established
439The Journal of General Physiology
° T H E J O U R N A L O F G E N E R A L P H Y S I O L O G Y • V O L U M E45 " ~962human cell lines and a primary rabbit kidney cortex tissue culture has been reported to be almost identical (4). Two hypotheses have been advanced to account for this uniformity (5). The first is that similarities between cell lines derived from various species and tissues may be due to the selection of a ubiquitous cell type which is best able to multiply in vitro. The second alternative is that the tissue culture environment may either influence different cell types to develop common nutritional and metabolic patterns, or during long term culture select a particular cell type from the initial population. By employing suitable environments, clonal lines with characteristics distinguishing them from the parent cultures may be isolated from human and animal cell cultures (6-10). Cultivation of mammalian cell lines in the presence of compounds having specific biologic actions, such as hormones, drugs, and inducers or repressors of specific protein synthesis might reveal different responses related to the tissue of origin. In particular, hormones are known to have different specific effects depending on the tissue an...
