X-Message-Number: 33102
Date: Sun, 05 Dec 2010 19:50:58 -0500
Subject: Re: could argon/xenon improve vitrification solutions?

I have some follow-up comments to the CryoNet
posting that I made yesterday:


in reference to the pressurized xenon clathrate
cryopreservation study:



I want to acknowledge that the electron micrographs
of the cardiomyocytes in the tissue specimens cut from
the mouse hearts cryopreserved in pressurized xenon-oxygen
look somewhat better to me than those cryopreserved in
pressurized nitrogen-oxygen. I have had little experience
interpreting electron micrographs, so my impressions
aren't worth much, however. I am willing to trust the
interpretations of the images given by the investigators.

I cannot explain why the pressurized xenon-oxygen sample
would show better images. The paper suggests that
clathrates formed in the cell reduce the amount of
extracellular ice by retaining water in the cell that
would otherwise have migrated across the cell membranes
during the freezing process, thereby protecting the
cardiomyocytes from dehydration damage. The paper
also suggests that the xenon clathrates are protecting
cells from recrystallization damage during the thawing
process. I note that if the latter explanation is
true, then the improved micrographs are not indicative
of improved structural preservation during cryostasis.

   The paper is critical of vitrification because
of cryoprotectant toxicity and another vaguely-referenced
source of injury (possibly devitrification). This is
given as a reason why a vitrified sample was not
prepared for comparison.

   As I wrote in my CryoNet posting yesterday,
vitrification and clathrate formation are incompatible
approaches to cryopreservation. Clathrates are
structures similar to ice, which means that vitrification
would prevent clathrate formation at least as
readily as it prevents ice formation.

        -- Ben Best

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