X-Message-Number: 7423
Date: Sun, 5 Jan 1997 02:38:59 -0800 (PST)
From: Doug Skrecky <>
Subject: Can the Visser Technique be Improved?

     In cryonet message 7415 Saul Kent revealed
 that the cryoprotectant used in the Visser technique is
 dimethylformamide. Apparently relatively low and nontoxic concentrations
 of this are used in conjunction with fast freezing to cryopreserve rat
 hearts without vitrification. A possible improvement in this technique
 might be achieved by choosing a different cryoprotectant or perhaps
 combination of cryoprotectants.
     When one examines the effect of cryoprotectants on subzero
 nonfreezing storage of rat hearts one finds an interesting correlation.
 The order of merit is methanol > ethanol > ethylene glycol > propylene
 glycol > glycerol. (1) It is interesting that this is also the same order
 ranking for the membrane permeability of these various substances. (2)
 Yet more effective cryoprotectants might be found in those with either a
 still greater membrane permeability or a lower toxicity. The later factor
 may be the reason polyethylene glycol is better at preserving function in
 frozen hearts than glycerol and why glucose is in turn better than
 polyethylene glycol at preserving unfrozen hearts at high subzero
 temperatures. (3) (4)
     The reason for the selection of dimethylformamide is obvious from the
 following table of relative membrane permeabilities: (all solutes with
 permeabilities greater than methanol are listed from reference 2)
 
     NAME     MEMBRANE PERMEABILITY
 glycerol             1
 methanol            19.6
 dimethylformamide   20.5
 dioxane             20.6
 ethylene glycol
    monomethyl ether 20.9
 ethylene glycol
    monoethyl ether  22.1
 dimethylacetamide   25.4
 monobutyrin         34.1
 diethylacetamide    36.2
 urea                41.1
 triethylene glycol
      diacetate      44.1
 pyridine            62.8

     Possible improvements in the cryoprotectant solution might accrue by
 considering solutes with permeabilities higher than dimethylformamide,
 possibily in combination with glucose.

 (1) Cryobiology 30:366-375 1993
 (2) The Journal of General Physiology 62: 714-736 1973
 (3) Cryobiology 29: 87-94 1992
 (4) Transplantation Proceedings 26(4) 2428-2430 1994


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