Phosphatidylserine Exposure in B Lymphocytes: a Role for Lipid Packing.
From: Medical Research council (MRC) Clinical Sciences Centre, Faculty of Medicine, Imperial College, Hammersmith Hospital Campus, Du Cane Rd, London, W12 0NN, United Kingdom. james.elliott@csc.mrc.ac.uk
Blood
- Publish Date: Sep 2006
- ISSN: 0006-4971
- Volume: 108
- Issue: 5
- Pages: 1611-7
- Medium: Print
- Language: English
- Citation (JAMA): Elliott James I, Sardini Alessandro, Cooper Joanne C, et al. Phosphatidylserine Exposure in B Lymphocytes: a Role for Lipid Packing.. Blood Sep 2006;108:1611-7
Abstract
Plasma membrane lipids are usually distributed asymmetrically, with phosphatidylserine (PS) confined to the inner leaflet. PS exposure at the outer leaflet occurs early in apoptosis, but it is also constitutive on some nonapoptotic cell populations where it plays a role in cell signaling. How PS is transported (“flopped”) to the cell surface is unknown. Contrary to previous reports that normal murine B lymphocytes lack lipid asymmetry, we show that PS is normally restricted to the inner leaflet of these cells. PS exposure on normal B cells did, however, occur spontaneously ex vivo. Consistent with the hypothesis that loss of PS asymmetry is regulated by CD45, PS is constitutively exposed on viable, CD45-deficient B cells. We show that calcium-stimulated PS exposure in B cells is strain variable, ABCA1 independent, and both preceded by and dependent on a decrease in lipid packing. This decrease in lipid packing is concomitant with cell shrinkage and consequent membrane distortion, both of which are potently inhibited by blockers of volume-regulatory K+ and Cl- ion channels. Thus, changes in plasma membrane organization precede PS translocation. The data suggest a model in which PS redistribution may occur by a translocase-independent mechanism at energetically favorable sites of membrane perturbation where lipid packing is decreased.
Mesh Headings (Keywords): Animals, B-Lymphocytes, Biological Transport, Flow Cytometry, Lipids, Lymphocyte Activation, Mice, Mice, Inbred C57BL, Phosphatidylinositols
Check for Full Text / PubMed Unique Identifier (PMID): 16684961
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