Membrane Lipid Fluidity and Filterability of Red Blood Cells from Adults and Newborns

Abstract

ABSTRACT. Membrane lipid fluidity was reexamined in red blood cells and ghosts from adults and newborns. Fluorescence anisotropies of the hydrophobic probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and perylene were significantly and substantially greater in fresh intact red cells from newborns than from adults; however, no significant difference was detected with the polar fluorophores, 12-(9-anthroyl) stearic acid and retinol. These results suggest that probes in the hydrophobic core of the membrane have less motional freedom in red cells from newborns than from adults, whereas probe motional freedom in the polar lipid headgroup regions of the membranes is similar for both cell types. DPH fluorescence anisotropy increased upon making white ghosts or upon storage of blood. Temperature studies indicated that DPH fluorescence anisotropy in fresh intact neonatal red cells is increased by an amount corresponding to that produced by cooling adult red cells by 22" C. Elevated intracellular calcium decreased red cell filterability without affecting DPH fluorescence anisotropy of ghost membranes. This result suggests that the effect of calcium in reducing filterability is independent of alterations in membrane lipid motional freedom. It is unlikely that the decreased lipid motional freedom of red cells from newborns contributes significantly to their decreased filterability. (Pediatr Res 24: 433-437, 1988) Abbreviations DPH, 1,6-diphenyl-1,3,5-hexatriene AS, 12-(9-anthroyl) stearic acid THF, tetrahydrofuran Hct, hematocrit C&, intracellular calcium C%, extracellular calcium femtin-conjugated concanavalin A induces endocytosis in red cells from newborns, but not in those from adults (1 1). One hypothesis proposed to explain this difference in endocytosis was increased lipid fluidity of neonatal red cell membranes. However, fluorescence polarization studies of Kehry et al.(1 2) revealed no difference in the motional freedom of perylene in ghost membranes prepared from outdated adult red cells, as compared with ghosts from fresh neonatal red cells. Other studies suggest that it may be inappropriate to conclude from the data of Kehry et al. (12) that membrane lipid fluidity is the same for red cells from newborns and adults for the following two reasons: 1 ) the comparison was made with ghost membranes, yet DPH fluorescence polarization is increased in ghosts as compared with intact cells (13); and 2) the ghosts from adult cells were prepared from outdated blood, yet storage of blood reportedly alters membrane lipid fluidity (14). Our report describes experiments that reexamined membrane lipid fluidity of fresh intact red cells from human newborns and adults using the more sensitive fluorophore DPH. The results indicate that the motional freedom of both DPH and perylene is actually less in fresh, intact red cells from neonates as compared with adults. Experiments with elevated Ca, demonstrated conditions under which fluidity and filterability are independent and uncorrelated parameters. A preliminary account of some of thes...

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