Characteristics of proliferative cells from young, old, and transformed WI 38 cultures.

Mitotic cells were obtained by a shake off procedure from cultures of normal WI 38 cells at various passage levels, and from SV-40 virus transformed cells. The size of all mitotic WI 38 cells was similar regardless of in vitro age, whereas cells from the monolayer displayed an age-related increase in size. Mitotic transformed cells were similar to normal in size, but no size changes were observed in transformed monolayer cells during serial passage. Ultrastructural studies of mitotic WI 38 cells revealed no consistent change in the numbers of mitochondria or lysosome-like bodies during aging in culture. Mitotic transformed cells displayed numbers of mitochondria comparable to normal cells, but lysosome-like bodies occurred less frequently. Size distribution and structural characteristic are presented in relation to the ability of cells to synthesize DNA and to divide. These results support the contention that aging in WI 38 cultures is characterized by a declining fraction of homogeneous, actively dividing cells, and an increasing fraction of heterogenous nondividers that display senescent changes.