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 (-5) M. At 37 degrees C, the presence of calcium for the first 20 min of exposure was suffcient to induce the EPM reduction, and Ca 2+ administration subsequent to Ca 2+ -free incubation for 30 min following irradiation had no effect on EPM. At lower temperatures, from 10 down to 20 degrees C however, the effect of calcium on the reduction of EPM decreased drastically. If the cells were kept Ca 2+ -inonophore A23187 also induced to decrease in EPM only in the presence of Ca 2+. These results revealed the transitory existence of membrane condition reactive to extracellular Ca 2+ immediately after X-irradiation, which can be postponed at low temperatures. The reduction of EPM by Ca 2+ -ionophore might suggest that the influx of Ca 2+ is a step in the reduction of EPM after X-irradiation.