Annexin V-FITC Labeling
Phosphatidylserine (PS) exposure at the outer plasma mem-
brane leaflet was measured in annexin-binding assay. Washed
erythrocytes were suspended (1 % Hct) in annexin-binding
buffer containing 140 mM NaCl, 2.5 mM CaCl2, and 10 mM
HEPES/NaOH (pH 7.4 at room temperature). Then the cells
were stained with FITC-annexin V (1:20) in the dark for
15 min, diluted with the same buffer to 0.01 % Hct and
subjected for flow cytometry. Flow cytometric analysis was
performed on EPICS XL cytometer (Beckman Coulter Inc.,
Brea, CA) using SYSTEM II (Version 3.0) software for acqui-
sition and analysis. Annexin V fluorescence intensity was mea-
sured in FL-1 channel set on logarithmic scale with 488 nm
excitation wavelength and 530 nm emission wavelength.