labeled with 5m l annexin V-fluorescein and 5m l PI in 100m l
of binding buffer (10mM HEPES/NaOH, pH 7.4, 140mM
NaCl, 2.5mM CaCl2). After 15 min incubation at room temperature,
400m l of binding buffer was added in each sample
and cells were then analyzed by a FACSCalibur flow cytometer
(BD Bioscience, San Jose, CA, U.S.A.) of 20000 cells
in each group. Annexin-V binds to those cells that express
phosphatidylserine on the outer layer of cell membrane.
This allows for the discrimination of living cells (unstained
with either fluorochrome) from apoptotic cells (stained
only with annexin-V) and necrotic cells (stained with both of
annexin-V and PI).16,17) Data analysis was performed with
the standard Cell Quest Software. All experiments were
performed in duplicate and reproducibility was checked in
three independent experiments.