Morphometric Changes as a Function of the Proliferative Status of Murine Mammary Carcinoma Cells

Ultrastructural analysis was performed to determine morphological changes in the 67 murine mammary tumor cells grown in four defined metabolic states in vitro, i.e., proliferating cells (P), cells in transition towards quiescence (T), nutrient-deprived quiescent cells (QI), and QI cells stimulated to reenter the cell cycle (St4) by refeeding for 4h in situ with complete medium. Also, these documented changes were evaluated as a function of the radiosensitivity of the various cell types. The average number of lipid body and mitochondrial profiles per cell was significantly higher in QI and St4 cells versus P cells. Also, greater variability was observed in the number of lipid bodies and mitochondria per cell section in the T, QI and St4 cells relative to P cells. Nuclear alterations involved little change in nuclear area occupied by heterochromatin in QI cells compared to P cells but the number of heterochromatin patches decreased in QI cells compared to P cells indicating a change in higher order chromatin packaging. The nucleolar organization was lost in QI cells as measured by the almost complete lack of nuclear area occupied by nucleoli in QI cells. In addition, nuclear diameter decreased in QI cells compared to P and T cells, but not St4 cells. The multiple changes in the morphological organization suggest a shift in the metabolic functioning of the cells relative to the proliferative status of the cell; however, there was no apparent correlation between these described changes and the respective radiation responses as measured by cell-survival analysis