Identification and characterization of non-dividing cell populations in phase II cultures of human glial cells.

It has been reported that cultures of normal cells in phase II contain a non-multiplying cell population, the size of which increases with passage number. In phase II cultures of normal human glial cells we have found two subpopulations of non-proliferating cells, one of which has a characteristic morphology, and differs from the actively dividing cells in a number of respects: (1) they are larger although of various sizes and are well spread over a very large substratum area: (2) they contain a great number of granules showing acid phosphatase activity, being heavy metal positive and displaying the characteristic natural fluorescence of lipofuscin pigment; and (3) they frequently contained a central somewhat irregular nucleus with various numbers of darkly staining nucleolar-like structures. Cytophotometric nuclear DNA measurements of the described "large" cell population show a decreased proportion of diploid cells as compared to their smaller sister cells. Moreover, with increasing passage number, the DNA values for large cells shift towards higher ploidy levels resulting in a scattered aneuploid pattern in the oldest passage. This "large" cell subpopulation consists of between 2% and 3% of all passages and becomes greatly decreased following subcultivation. The other subpopulation of non-dividing cells is generally morphologically similar to the dividers, increases in size with passage number and is the more important in the phase III phenomenon.