Gamma irradiation of RBCs results in the production of reactive oxygen capable of initiating the process of membrane lipid peroxidation and accelerates the leakage of potassium ions from RBCs, resulting in an increase of internal viscosity. The elastic properties of irradiated and stored RBC units were studied using laser optical tweezers. The laser trapped the cell and the membrane elasticity was analyzed, measuring the cell deformation in six different drag velocities. Five RBC units were split into two portions. One portion received a gamma irradiation dose of 25 Gy, and the second one was used as a control and was not irradiated. All units were stored (4 degrees C), and the elasticity was examined on Days 1, 14, 21, and 28. Elastic properties (mu) from irradiated RBCs stored for 21 and 28 days were significantly affected compared with control cells (21 days: control, 0.3 +/- 0.03 x 10(-3); irradiated, 3.5 +/- 1.3 x 10(-3) dyn/cm; p < 0.001; and 28 days: control, 0.5 +/- 0.09 x 10(-3); irradiated, 14 +/- 3.2 x 10(-3) dyn/cm; p < 0.001). The sensitivity of the laser optical tweezers method showed that there is no significant change in elasticity over time for up to 14 days of storage, regardless of whether the unit was irradiated or not. However, beyond 21 days of storage, irradiated units demonstrate decreased elasticity.421196-9