No elevated cell surface charge at mitosis in X-ray-irradiated mammalian cells.

Abstract

ABSTRACT. Rounded mitotic cells showed 30 % enhanced electrophoretic mobility (EPM) when compared to spindle-formed interphase cells. This increase in EPM that was not present in interphase cells that had been rounded chemically by EDTA is considered to reflect a structural change in the cell membrane during mitosis. X-ray irradiation induced a dose-dependent EPM decrease in both interphase and mitotic cells during a 4-hour period. During the next 20 h of incubation, EPM recovery took place in cells irradiated with 250R, but not in cells exposed to 1000R. EPM was enhanced during mitosis in cells irradiated with low doses, but was absent in cells irradiated with 1000R. The ratio of colony-forming cells and of electrophoretically recovered mitotic cells after 24 h of exposure showed a good statistical correlation. These results indicate that unrepaired membrane damage contributes to mitotic cell death after irradiation.We used an electrophoretic assay to investigate membrane damage to cells that showed impaired proliferation and death after X-ray irradiation. The advantages of our method are its high sensitivity as a probe for detecting alterations in the dynamic physiological charge-related properties on the surface of living cells (6, 11, 15) and the simultaneous detection of electrophoretic mobility (EPM) and the morphology of individual cells under phase microscopy.Decreases in EPM after irradiation have been reported in several types of mammalian cells and in yeasts (19, 20, 25). Our previous studies of three lines of cultured mammalian cells showed that the percent of cells whose EPM did not recover within 24 h after irradiation agreed statistically with the ratio of non-colony forming cells (23, 24,26). Our first studies of the relation between cell division and the cell surface charge on individual cells used Escherichia coli as the model system. E. coli, which is inhibited during cell division, is visible during EPM measurements because of its filamentous form. The results for E. coli indicated that EPM decreased in cells whose division was inhibited and that recovery took place when cell division was resumed (30).Since Spear and Glticksmann's 1938 report, the common belief has been that cellular death is associated with mitosis after X-ray irradiation. Irradiation does not result in immediate death, it is delayed until the first mitosis after irradiation (40).