ISSN:
1432-1424
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Summary A central tenet in cryobiology is that low-molecular-weight protective solutes such as glycerol must permeate cells in high concentration in order to protect them from freezing injury. To test this supposition, it is necessary to estimate the amount of solute that has permeated a cell prior to freezing. The amount in bovine red cells was estimated from the flux equation $${{ds} \mathord{\left/ {\vphantom {{ds} {dt}}} \right. \kern-\nulldelimiterspace} {dt}} = P_\gamma A[(activity external solute) - (activity internal solute)].$$ Solving the equation required estimates ofP γ, the permeability constant for the solute. Estimates for glycerol in bovine red cells were made in two ways: (1) by measuring the time to 50% hemolysis of red cells suspended in isosmotic or hyperosmotic (1 to 3m) solutions of glycerol that were hypotonic with respect to NaCl, and (2) by measuring the time required for red cells in hyperosmotic solutions of glycerol in isotonic salinebuffer to become susceptible to osmotic shock upon 10-fold dilution with isotonic saline-buffer. The measurements were made at 0, 10, 15 and 20°C. The values by the second technique ranged from 2.3×10−6 cm/min to 2.7×10−6 cm/min at 20°C, depending on the concentration of glycerol. The values by the first technique were 0 to 30% lower. Both techniques yielded about the same activation energy for permeation between 0 and 20°C, 21 kcal/mole. This is equivalent to a halving of the permeation rate for every 5° drop in temperature. Expressing the flux equation in the formulation of irreversible thermodynamics changed the value ofP by less than 10%, probably because σ, the reflection coefficient, is 0.95 at 25°C. Expressing the driving force as the difference in molality or osmolality of glycerol, rather than as the difference in activity, however, had somewhat greater effects on the numerical values ofP, but had no effect on the activation energy. It is concluded that estimates ofP based on differences in activities and on the osmotic shock technique are the least subject to error. The use of the usual irreversible thermodynamic equations to express the flux may be a misleading refinement, in that the assumptions underlying them become questionable for concentrations of glycerol as high as 1, 2, or 3m.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01870084
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