Rat erythrocytes and their ghosts were utilized to investigate the target and mechanism of the reported decrease in electrophoretic mobility (EPM) of cultured mammalian cells after exposure to X radiation. Similar dose-dependent reductions in EPM's were observed in both whole erythrocytes and their ghosts. Recovery of EPM was evident in whole erythrocytes after irradiation with doses lower than 500 R, but was lacking in ghosts. This suggests that the cell membrane itself is the target of X irradiation with respect to EPM reduction, and that a cytoplasmic factor is necessary for the recovery. The amount of sialic acid did not decrease after irradiation. By using phosphate buffers of different ionic strengths, which determines the effective thickness of the ion atmosphere for EPM, dislocation of sialic acid from the peripheral zone of 0-7.5 Å to a deeper zone of 9.7-17 Å was suggested. The decrease in EPM was independent of temperature in the range 22-37°C, but was markedly influenced by temperature between 10 and 20°C. This temperature dependence of EPM was similar to that of the fluidity of membrane lipid, which determines the facility in the rearrangement of membrane components.

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