Blood, Vol. 94 No. 1 (July 1), 1999:
pp. 319-325
Hereditary Spherocytosis and Elliptocytosis Erythrocytes Show a Normal
Transbilayer Phospholipid Distribution
Kitty de Jong,
Sandra K. Larkin,
Stefan Eber,
Paul F.H. Franck,
Ben Roelofsen, and
Frans A. Kuypers
From Children's Hospital Oakland Research Institute, Oakland, CA;
Kinderklinik, Georg-August University Göttingen, Göttingen,
Germany; Centraal Klinisch Chemisch Laboratorium, Ziekenhuis Leyenburg,
Den Haag, the Netherlands; and Centre for Biomembranes and Lipid
Enzymology, University of Utrecht, the Netherlands.
Phosphatidylserine (PS) asymmetry was determined in red blood cells
from patients with hereditary spherocytosis and elliptocytosis. No
PS-exposing subpopulations were detected using the very sensitive method with fluorescently labeled annexin V. Treatment with
N-ethylmaleimide or adenosine triphosphate (ATP) depletion to
inactivate the flipase did not lead to formation of PS-exposing
subpopulations in these cells, but elevated intracellular calcium
levels did lead to extensive scrambling of the PS asymmetry. Although
interactions of the membrane skeleton with the phospholipid bilayer
have been suggested to stabilize the asymmetric distribution of PS
across the bilayer, our data show that red blood cells with a severely
damaged membrane skeleton are able to preserve asymmetry, even under
conditions in which restoration of the asymmetric distribution is
excluded. Moreover, the loss of membrane asymmetry in these cells
requires active scrambling involving high levels of intracellular
calcium as in normal cells. Our data show that the severe disorder of the membrane skeleton found in these cells does not affect the activity
of flipase or scramblase, indicating that these proteins are not
regulated by, nor coupled to the membrane skeleton assembly, and that
possible thrombotic events in spherocytosis patients are not likely
associated with altered PS topology of the red blood cells.
