Impaired fetal erythrocytes' filterability: relationship with cell size, membrane fluidity, and membrane lipid composition.

The lipid composition of erythrocytes (red blood cells [RBCs]) plays a significant role in determining certain membrane biophysical properties. We have found that fetal RBCs showed a dramatically low filterability compared with adult RBCs and questioned whether this could be a consequence of their membrane lipid composition. We therefore studied fetal RBCs at two different gestational ages, neonatal RBCs and adult RBCs. Biophysical parameters were studied using two different techniques, filterability and membrane fluidity. The latter was measured by fluorescence polarization using three different probes. The membrane lipid composition was examined by measuring cholesterol and phospholipids. After extraction of the phospholipids, followed by high performance thin-layer chromatography, the fatty acids in the phospholipid subfractions were analyzed by gas-liquid chromatography. The fetal RBCs' filterability was found to be correlated with both the larger size and the higher hemoglobin content of the cells, but there was no correlation between RBC filterability and fluidity or membrane lipid composition. In adult RBCs, compared with neonatal RBCs, the slight increase of unsaturated fatty acids in phosphatidylcholine and phosphatidylethanolamine should have increased the membrane fluidity. However, in RBCs, no change was observed in the fluidity parameters measured by fluorescence polarization.