Heavy ion induced membrane damage: hemolysis of erythrocytes and changes in erythrocyte membrane fluidity.

Human erythrocytes were irradiated with heavy ions of energies between 4 and 18 MeV/u having linear energy transfer (LET) values between 92 and 14,000 keV/microns. Hemolysis has been studied as a macroscopic parameter for membrane damage and changes of the fluidity as a more microscopic parameter. The membrane fluidity changed in a characteristic dose-dependent manner as detected by electron spin resonance employing 12-doxylstearic acid methyl ester spin label (SL 12). Lysis cross sections and RBE values were determined from dose effect curves. The results demonstrate a high hemolytic efficiency of heavy ions compared to X rays. With increasing LET values the measured relative biological efficiency (RBE) values increase continuously. In the complete LET range the cross sections formed one common curve as function of LET and no saturation effects are observed. This is in direct contrast to other biological endpoints such as cell inactivation or DNA damage.