Calcium-dependent Process in Reduction of Cell Surface Charge after X-irradiation

Summary

The electrophoretic mobility (EPM) of rat erythrocytes and cultured melanoma cells decreased with time after X-irradiation in the presence of calcium at concentrations higher than 10⁻⁵ M. At 37°C, the presence of calcium for the first 20 min of exposure was sufficient to induce the EPM reduction, and Ca²⁺ administration subsequent to Ca²⁺-free incubation for 30 min following irradiation had no effect on EPM. At lower temperatures, from 10 down to 20°C however, the effect of calcium on the reduction of EPM decreased drastically. If the cells were kept Ca²⁺-free at 3°C after irradiation, the later addition of calcium at 37°C induced the EPM reduction. Ca²⁺-ionophore A23187 also induced the decrease in EPM only in the presence of Ca²⁺.

These results revealed the transitory existence of a membrane condition reactive to extracellular Ca²⁺ immediately after X-irradiation, which can be postponed at low temperatures. The reduction of EPM by Ca²⁺-ionophore might suggest that the influx of Ca²⁺ is a step in the reduction of EPM after X-irradiation.