The complex of phosphatidylinositol 4,5-bisphosphate and calcium ions is not responsible for Ca2+-induced loss of phospholipid asymmetry in the human erythrocyte: A study in Scott syndrome, a disorder of calcium-induced phospholipid scrambling

Edouard M. Bevers, Therese Wiedmer, Paul Comfurius, Ji Zhao, Edgar F. Smeets, Robert A. Schlegel, Alan J. Schroit, Harvey J. Weiss, Patrick Williamson, Robert F A Zwaal, Peter J. Sims

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46 Scopus citations

Abstract

Elevation of cytoplasmic Ca2+ levels in human erythrocytes induces a progressive loss of membrane phospholipid asymmetry, a process that is impaired in erythrocytes from a patient with Scott syndrome. We show here that porcine erythrocytes are similarly incapable of Ca2+-induced redistribution of membrane phospholipids. Because a complex of phosphatidylinositol 4,5-bisphosphate (PiP2) and Ca2+ has been proposed as the mediator of enhanced transbilayer movement of lipids (J Biol Chem 269:6347,1994), these cell systems offer a unique opportunity for testing this mechanism. Analysis of both total PIP2 content and the metabolic- resistant pool of PIP2 that remains after incubation with Ca2+ ionophore showed no appreciable differences between normal and Scott erythrocytes. Moreover, porcine erythrocytes were found to have slightly higher levels of both total and metabolic-resistant PIP2 in comparison with normal human erythrocytes. Although loading of normal erythrocytes with exogenously added PIP2 gave rise to a Ca2+-induced increase in prothrombinase activity and apparent transbilayer movement of nitrobenzoxadiazolyl (NBD)-phospholipids, these PIP2-loaded cells were also found to undergo progressive Ca2+- dependent cell lysis, which seriously hampers interpretation of these data. Moreover, loading Scott cells with PIP2 did not abolish their impaired lipid scrambling, even in the presence of a Ca2+-ionophore. Finally, artificial lipid vesicles containing no PIP2 or 1 mole percent of PIP2 were indistinguishable with respect to transbilayer movement of NBD- phosphatidylcholine in the presence of Ca2+. Our findings suggest that Ca2+-induced redistribution of membrane phospholipids cannot simply be attributed to the steady-state concentration of PIP2, and imply that such lipid movement is regulated by other cellular processes.

Original languageEnglish (US)
Pages (from-to)1983-1991
Number of pages9
JournalBlood
Volume86
Issue number5
DOIs
StatePublished - 1995

ASJC Scopus subject areas

  • Biochemistry
  • Immunology
  • Hematology
  • Cell Biology

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