Changes in cell volume and internal sodium concentration in HeLa cells during exponential growth and following ionidamine treatment

Cell volumes decreased in HeLa cells as a function of time after seeding du ring exponential growth. Cell volume distributions revealed the presence of two cell populations in all stages of growth. When cells approached conflu ence, the ratio of the two populations abruptly shifted towards that charac terised by the smallest volume. Percentages of G1-, S- and G2 + M-phase cel ls were also measured and it was found that GI frequency increased as a fun ction of cell density during exponential growth. Intracellular sodium conce ntration, [Na](i) was monitored by Na-23 NMR in the presence of 5 mM dyspro sium (III) tripolyphosphate. [Na](i) increased from 22.8 to 59.0 mM in cell s from the second to the seventh day after seeding, Treatment with lonidami ne, an antitumoral drug that it is known to slow down cell growth by affect ing aerobic glycolysis, produced a complete block of cell progression after a few days of treatment. The progression of cell volume distributions towa rds smaller volumes and the increase in internal sodium concentration as a function of time after seeding were also affected by the drug. These phenom ena were related to the existence of a subpopulation of mitotically inactiv e G1-phase cells during exponential growth, pointing out that a density-dep endent cellular mechanism regulates the cell cycling in HeLa cells.