Thermosensitivity of red blood cells from Down's syndrome individuals

Biochemical disturbances of the reactive oxygen species metabolism revealed in subjects with Down's syndrome (DS), and the findings indicating that heat-induced cell alterations have been, at least, partly mediated by reactive oxygen species, made the elucidation of the response of trisomic cells to elevated temperatures of special interest. Kinetic analysis of cell-survival curves, accompanied by the flow cytometry and the scanning electron microscopy (SEM) examinations, and their relationship with the cell membrane fluidity, were undertaken. At each temperature (48-54 degrees C), Dq parameters, representing the ability to accumulate sublethal damages, were similar for both cell groups. D0 parameters (inverse leakage rates; D0 = 1/k) were greater for DS cells at each temperature below 54 degrees C. The haemolysis sensitivity ratio (HSR) showed that DS erythrocytes were, in average, 1.60 times more resistant to heat injury than those from normal subjects. Activation energies of haemolysis, calculated according to the Arrhenius equation, were similar both for normal (290.8 +/- 6.5 [kJ/mol]) and DS erythrocytes (288.0 +/- 5.5 [kJ/mol]). Flow cytometry studies showed that the scattering properties of intact DS erythrocytes (reflecting size, volume, shape and cell membrane surface morphology) were different than those of normal cells. Scanning electron micrographs and scattering diagrams obtained for cells submitted to heat stress (51 degrees C) confirmed that DS erythrocytes were more resistant, to a certain extent, to heat-induced disruption than normal cells. The steady-state fluorescence anisotropy of TMA-DPH (1-(4-trimethyl-ammoniumphenyl)-6-phenyl-1,3,5-hexatriene) showed that untreated DS erythrocytes had substantially lower fluidity (r = 0.356 +/- 0.008) of the outer monolayer of cell membranes as compared to normal cells (r = 0.324 +/- 0.011). The increase of the cell membrane fluidity during exposure to heat was observed. The greatest elevation of cell membrane fluidity occurred during the preleakage period, immediately upon the heat treatment and was considered as a rate-limiting step of heat-induced haemolysis.