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

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Abstract
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.