Abstract
Red Blood Cells (RBC's) of human newborns have a number of different characteristics from those of adults. In order to increase understanding of these differences, membrane lipid fluidity (MLF) as indicated by the fluorescence polarization of diphenylhexatriene (DPH) and filterability(F) as a gross measure of cell deformability were compared in the presence and absence of calcium. DPH fluorescence polarization in fresh intact cells from adults was 0.282±.011(S.D.n=14), significantly less than 0.327±0.010(S.D.,n=7) in newborns. While quantitative estimates from DPH fluorescence polarization are subject to uncertainties, the results suggest decreased fluidity in the hydrophobic core of red cell membranes of newborns. This is consistent with the greater proportion of saturated fatty acids in RBC membranes from newborns.Treating RBC's from adults with 1μM Ca ionophore A23187 at 5 mMCaCl2, decreases F by 49±12%(S.D. ,n=4). In contrast MLF of RBC's is unchanged with 1μM A23187 and 5 mMCaCl2. RBC's from newborns exhibit decreased F at O mM and 5 mMCa in comparison with RBC's from adults. Experiments with Ca demonstrate conditions under which F and MLF are independent and uncorrelated parameters. When Ca induces echinocytosis and decreases F it does so without causing bulk changes in the hydrophobic core of the membrane. Ca must exert its effects either on the polar lipid headgroups or on the cytoskeletal proteins.
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