Dead Cell Marker on 633 nm tom_frey at
Fri Nov 8 06:38:40 EST 1996

In response to professor Kell's post, I advance the following personal 

>> I have used  TO-PRO-3 as  live dead discriminator with red 
>> excitation.  Note that the -3 is important, Molecular Probes 
>> also sells TO-PRO-1!  For TP3, saturating concentration is 2-4 uM.  

> I'll say.....esp. in view of what follows. How much DNA stain do
> people want to whack about, on the reasonable asumption that that
> which binds to DNA may not be frightfully good for it?

To clarify, by saturating I meant "I use it to get best CVs when staining
nuclei or fixed and permabilized cells for DNA content/cell cycle"

> Out of interest, what is here the  'gold standard'? We in Aber are
> beginning to have suspicions that supposedly pure(ish)  TO-PRO[3],
> or likely a metabolite / degradation product thereof, penetrates (and
> ergo stains) ""live"" [i.e. not all that knackered] cells (bugs). 
> What say you, and netters to whom this is copied?

I mention in passing in Cytometry 21:265 that TO-PRO-3 enters apoptotic 
thymocytes more rapidly than the normal cells in the same sample.  PI and EB 
are well know to behave the same.  While "apoptotic" may or may not mean 
something to bugs, I would hesitate to suggest problems with TO-PRO-3 unless
I knew that PI and EB do not show the same effect.  You may, of course, 
know this.

This does suggest my opinion of a gold standard.  TO-PRO-3 is only available 
from Molecular Probes, and should be compared to similar molecules like ethidium 
and propidium which have long histories and multiple sources.

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