Carol Johnson wrote- >Contrary to a variety of posts to this list, while paraformaldehyde does >indeed >kill cells, it does not necessarily permeabilize them enough to allow PI into >all of the cells. For rat bone marrow cells, less than 25% of the cells >take up >PI following 0.5% paraformaldehyde fixation (as evaluated under a fluorescent >microscope), even though 100% of the cells are indeed dead. Additional >permeabilization is needed to make all the cells pick up the dye. > >There may be some variability between cell lines, etc. It is ALWAYS best to >actually look at the cells when a new method is tried. That's a good point, which I neglected to mention in my posting in reply to Mario Roederer. Let me reiterate that membrane permeability to dyes such as propidium is getting to look a lot more complicated than it did at first. And paraformaldehyde is not the only fixative that doesn't always permeabilize cells (time and concentration, as well as cell type are issues to be considered for all fixatives). -Howard
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