The binding of Annexin V to phosphatidylserine is calcium dependent and very tight with a Kd of approximately 5 x 10-10 M, consequently, your Annexin V buffer must have calcium in it to see Annexin V binding. If you're using regular staining buffer or PBS to label your cells, you should not expect to see any Annexin V binding as regular staining buffer or PBS usually does not contain calcium.

On Feb 9, 2007, at 3:54 PM, Xiao Qun Zhai wrote:

Hi,

I am doing cell apoptotic/necrotic analysis using Annexin V/PI staining method. Very interestedly, my samples do not show early apoptotic population, which is Annexin V +ive/PI -ive. I am wondering why? Is this related to cell type? I can't see any early apoptotic cells in all my samples (control samples, high and low drug concentration treated samples). Has anyone here met the same problem? How to bring the early apoptotic population back?

Many thanks

Sunny Zhai

Lancashire School of Health and Postgraduate Medicine
Harrington Building
University of Central Lancashire
UCLAN
Preston
PR1 2HE
UK