Red blood cell (RBC) swelling and membrane hole formation in hypotonic external media were studied by measuring the time-dependent capacitance, C, and the conductance, G, in the beginning of the beta-dispersion range. At high and moderate osmolarities of the external solution the capacitance reaches a steady-state whereas at low osmolarities it reveals a biphasic kinetics. Examination of RBC suspensions exposed to different concentrations of HgCl(2) demonstrates that water transport through mercury-sensitive water channel controls RBC swelling. Unlike the capacitance, an increase in the conductance to a stationary level is observed after a certain delay. A comparison of G(t) curves recorded for the suspensions of the intact cells and those treated with cytochalasin B or glutaraldehyde demonstrates the significant effect of the membrane viscoelasticity on the pore formation. It is shown that the stretched membrane of completely swollen RBC retains its integrity for a certain time, termed as the membrane lifetime, t(memb). Therefore, the resistivity of RBCs to a certain osmotic shock may be quantified by the distribution function of RBC(t(memb)).

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In order to clarify the mechanism of dextran-induced aggregation, the effect of the ionic strength (I) on the minimal shear stress (tau(c)) required to rupture RBC doublets was studied for suspensions with the external media containing 76 and 298 kDa dextrans. At low and high ionic strengths, tau(c) increases with increasing I, whereas at intermediate I values, tau(c) versus I dependencies reveal a plateau step. The non-monotonous shape of these curves disagrees with the depletion model of RBC aggregation and is consistent with the predictions of the bridging mechanism. Literature reports point out that elastic behavior of dextran molecules in low and high I regions is fairly typical of Hookean springs and hence predict an increase in tau(c) with increasing I. A plateau step is accounted for by the enthalpic component of the dextran elasticity due to the shear-induced chair-boat transition of the dextran's glucopyranose rings. A longer plateau step for suspensions with a higher molecular weight dextran is explained by a larger contribution of the enthalpic component to the dextran elasticity. Thus, the results reported in this study provide evidence that RBC aggregation is caused by the formation of dextran bridges between the cells.

Human erythrocytes suspended in plasma, or in phosphate buffered saline (PBS), were exposed to ionizing radiation. Potassium leakage from irradiated erythrocytes is significantly higher in PBS than in plasma. The potassium leakage decreases when PBS is gradually replaced by plasma. These findings suggest that some of the plasma constituents have radioprotective properties. The potassium leakage per cell is independent of the hematocrit, Hct. The potassium leakage is attributed to the formation of radiation defects in the membrane. Analysis of the effect of radiation dose, plasma and cell concentrations on the product of the number and surface area of the radiation defects indicates that the radiation damage is mainly due to the direct formation of free radicals in the cell membrane. The radioprotective effect of plasma is attributed to surface reactions of these free radicals with plasma constituents adsorbed on the membrane.