We found propidium iodide not to be fixable in mammalian cells. It gets
trapped to some extent, however. PI is better retained in bacteria after
fixation. If you need a DNA dye to detect cells with permeable membranes,
that is fixable, you may try to use ethidium monoazide bromide. This dye is
UV-photocross-linkable. After a blast with UV, this dye should be bound
covalently to the DNA. I have myself not actually done this, therefore my
pre-empting statements. This dye is available from Molecular Probes, Inc.
(catalog # 1374); P.O. Box 22010; Eugene; OR 97402; tel: (541) 465-8300.
Martin Poot