Calcium-dependent process in reduction of cell surface charge after X-irradiation

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 10-5M. At 370C, 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 200C however, the effect of calcium on the reduction of EPM decreased drastically. If the cells were kept Ca2+-free at 30C after irradiation, the later addition of calcium at 370C 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. (author)