Tomas, Fixation will eliminate the barrier to PI entering the cell. But fixed cells are dead, so should stain anyway. You need to add the PI before fixation. Some may suggest that PI is retained (somewhat) following fixation. I don't know that I believe this . . . I'd have to try this and see. If you are interested in detecting cells that were dead prior to fixation, use EMA. See: "Riedy MC, et.al. Use of a Photolabeling Technique to Identify Nonviable Cells in Fixed Homologous or Heterologous Cell Populations. Cytometry 12:133-139, 1991." MAK. -- Mark A. KuKuruga, Managing Director University of Michigan Flow Core 7416 CCGC 0946 (734) 647-3216, fax (734) 936-7376 kukuru@umich.edu >>> "Tomas Corcoran" <mascor@gofree.indigo.ie> 04/17/01 02:44PM >>> I wonder whether anyone has experience or opinions on this : Does 0.5-2 %paraformaldehyde fixation of endothelial cells or tumour cells permeabilise cells to PI or not.Different sources say yes and no , but we have found that after removal of adherent cells from culture plates with 2mM EDTA and fixation that almost all cells stain with PI . Does paraformaldehyde fixation preclude meaningful viability assessment or not . Many thanks. mascor@gofree.indigo.ie
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