Irreversible loss of negative surface charge and loss of colony-forming ability in Burkitt lymphoma cells after x-irradiation

The electrokinetic behavior of Burkitt lymphoma P 3H-R1 cells were studied following X-irradiation. The surface charge of irradiated cells decreased progressively with time after X-ray treatment, as compared with a mean mobility value (−0.677 ± 0.045 μsec⁻¹ V⁻¹ cm) of non-irradiated cells. The frequency distribution of cells treated with 3 000 R 4 h previously showed quite a different peak of lower mobility than that of non-irradiated cells with the boundary of −0.550 μsec⁻¹ V⁻¹ cm. Percentages of cells which showed the higher mobility than the boundary value 4 h after irradiation with 30, 50, 65, 100, 200 or 3 000 R were in accord with the percentage of cells which showed colony-forming ability in soft agar, respectively. Following cell proliferation the population of electrokinetically intact cells increased with time after irradiation; these values also coincided with the population of colony-forming cells. Thus, the present results indicate that there is a close relation between loss of negative surface charge and loss of colony forming ability in irradiated cells, suggesting that loss of colony forming ability of the cells may be determined as early as 4 h after irradiation.     

Changes of the cell surface charge of amphibian ectoderm after induction

Summary Isolated ectoderm of early gastrula stages ofTriturus alpestris was treated with vegetalizing factor for 24 h employing the sandwich method (induced ectoderm). Controls were incubated for the same period with -globulin which has no inducing activity. Explants of both series were labelled with cationized ferritin, which binds to negatively charged groups at physiological pH. In non-induced ectoderm, ferritin particles can be found as a thin layer all over the plasma membranes. In induced ectoderm the total amount of ferritin bound to the plasma membrane is much lower than in non-induced ectoderm. Ferritin is located in restricted areas only. In contrast to the controls, other membrane areas are free of ferritin particles. The correlation between these results and the change of cell affinity after induction with vegetalizing factor is discussed.     

Possible reduction of surface charge by a mutation inParamecium tetraurelia

Summary Under voltage clamp, a mutant ofParamecium tetraurelia (teaB) shows a shift in the positive direction of the voltage sensitivity of the Ca conductance and the depolarization inactivation curve by 10 mV with no change in the total conductance. This effect can be mimicked in the wild type by the addition of external Ca²⁺ or Mg²⁺. The mutation also shifts the resting potential and the voltage sensitivities of the delayed rectification (depolarization-sensitive) K conductance and the anomalous rectification (hyperpolarization-sensitive) K conductance in the positive direction to a similar extent. This systematic shift of channel voltage sensitivities is best explained by the reduction of the surface negative charges of the membrane due to the mutation.     

Size-dependent mobile surface charge model of cell electrophoresis

A model that accurately predicts the effects of cellular size and electric field strength on electrophoretic mobility has been developed. Previous models have predicted that electrophoretic mobility (EPM) is dependent only on cell surface charge, bath viscosity and ionic strength of the electrolyte. However, careful analysis of experimental data from the literature shows that these models do not accurately depict the relationship between chemically determined surface charge and observed mobility. We propose a new model that accounts for electrically driven redistribution of mobile surface charge islands, such as the recently proposed lipid raft structures. This model predicts electrophoretic mobility as a function of a new dimensionless quantity, A, that incorporates the cell radius, the electric field strength, and the average diameter of charged membrane complexes.     

Protection after x-irradiation by 1,4-dithiothreitol of two mammalian cell types in vitro

1,4-Dithiothreitol (DTT) was found to diminish the amount of chromosomal breakage in leucocyte cultures of the marsupial Potorous tridactylus and in the Don strain of Chinese hamster cells (LHI). The maximum decrease of damage in Potorous lymphocytes was to 54% of that of the irradiated cells without DTT treatment, and to 64% in the case of the Chinese hamster cells. For both cell types, it was shown that the most significant effect of DTT was due to its presence in the first 30 min post irradiation. The protective action of this sulphydryl compound occurred even when DTT was not present during irradiation but was introduced as soon as possible after the X-ray dose was delivered.     

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

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.