Hereditary spherocytosis and elliptocytosis erythrocytes show a normal transbilayer phospholipid distribution

Phosphatidylserine (PS) asymmetry was determined in red blood cells from pa tients with hereditary spherocytosis and elliptocytosis. No PS-exposing sub populations were detected using the very sensitive method with fluorescentl y labeled annexin V. Treatment with N-ethylmaleimide or adenosine triphosph ate (ATP) depletion to inactivate the flipase did not lead to formation of PS-exposing subpopulations in these cells, but elevated intracellular calci um levels did lead to extensive scrambling of the PS asymmetry. Although in teractions of the membrane skeleton with the phospholipid bilayer have been suggested to stabilize the asymmetric distribution of PS across the bilaye r, our data show that red blood cells with a severely damaged membrane skel eton are able to preserve asymmetry, even under conditions in which restora tion of the asymmetric distribution is excluded. Moreover, the loss of memb rane asymmetry in these cells requires active scrambling involving high lev els of intracellular calcium as in normal cells. Our data show that the sev ere disorder of the membrane skeleton found in these cells does not affect the activity of flipase or scramblase, indicating that these proteins are n ot regulated by, nor coupled to the membrane skeleton assembly, and that po ssible thrombotic events in spherocytosis patients are not likely associate d with altered PS topology of the red blood cells. (C) 1999 by The American Society of Hematology.