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Dear Steve, 

I have used PKH26 (Sigma Aldrich) to label platelets for both in vitro and in vivo (injected in mouse) experiments. It works well, the platelets are still functional and the signal is really bright (565 nm excitation) and lasts long time. They also have the green version, which I have not tried yet.

In vivo tracking of platelets: circulating degranulated platelets rapidly lose surface P-selectin but continue to circulate and function.
Michelson AD1, Barnard MR, Hechtman HB, MacGregor H, Connolly RJ, Loscalzo J, Valeri CR.

Best wishes,

Ana (Oxford University, Dpt. Oncology)
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From: Confocal Microscopy List [[log in to unmask]] on behalf of Steve [[log in to unmask]]
Sent: 04 April 2014 19:57
To: [log in to unmask]
Subject: membrane-targeted fluorophores

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I have used membrane-targeted fluorophores for visualizing neuronal morphology
off and on over the years. Some colleagues have warned me about their potential
side affects, and although I have always been cautious of this I have not
experienced this until just recently. I also have never seen a publication that
describes these effects.

In my setup I have been using a membrane-targeted form of citrine I made by
adding the Ras CAAX prenylation site to the C-term of citrine. Unless it is
expressed at very low concentrations it causes both obvious morphological
defects, and leads to early cell death. I have used a similarly made version of
Venus which has a very similar sequence, and not seen these effects, though in a
slightly different experiment.

Does anyone have more knowledge of what membrane-targeted fluorophores are
best. I am considering using a palmitoylation sequence since I have it on hand,
but am not sure if that will help. Not sure if it is the fluorophore, the linker or the
lipid modification that leads to the problem, and am just generally curious what
other people think.