Water transport and estimated transmembrane potential during freezing of mouse oocytes

Abstract

The kinetics of water transport and the changes in transmembrane potential during freezing of mouse oocytes in isotonic phosphate buffered saline (PBS) were simulated using thermodynamic models. The permeability to water at 0 degree C, Lpg, and the activation energy, ELp, of metaphase II mouse oocytes from B6D2F1 mice were determined to be 0.044 +/- 0.008 micron/min-atm and 13.3 +/- 2.5 kcal/mol during freezing at 2 degrees C/min. The inactive cell volume was determined to be 0.214 with a correlation coefficient of 0.995, indicating that the oocytes closely follow the ideal Boyle-van't Hoff relation. The mean value of the oocyte diameter was 79.41 +/- 4.62 microns. These results were used to predict the behavior of mouse oocytes under various freezing conditions. The effect of the cooling rate on the cell volume and cytoplasm undercooling was investigated. The changes in transmembrane potential were also investigated during freezing of mouse oocytes. The computer simulations showed that at the beginning of the freezing process (-1 degrees C), the fast growth of ice in the extracellular solution causes a sharp increase of the membrane potential. It is predicted that the change in membrane potential is substantial for almost all cooling rates. Estimations show that values as high as -90 mV may be reached during freezing. The hyperpolarization of the membrane may cause orientation of the dipoles within the membrane. For membrane proteins with 300 debye dipole moment, the theoretical prediction suggests that the percentage of dipoles aligned with the membrane potential increases from 16% at 0 degrees C prior to freezing to 58% at -8 degrees C after seeding of the external ice followed with a cooling at 120 degrees C/min.

Transport phenomena during freezing of isolated hepatocytes

“…Satisfactory agreement between theoretical predictions and experimental observations for a wide range of conditions supports the validity of the proposed model and its underlying assumptions. used in our laboratory for other cell types with reasonable predictions Toner et al, 1990b). Another possible reason for the high values for ELp could involve subzero membrane damage which presumably would result in salt transport (countercurrent to the water transport) from outside to inside the cell.…”

“…1 includes a number of assumptions which have been a subject of extensive research in the field of cryobiology for the past two decades (Mazur, 1963;Mansoori, 1975;Levin et al, 1979;Shabana and McGrath, 1988;Toner et al, 1990b). The effect of a linear relationship rather than a 2/3 power dependence of A upon Vas in Eq.…”

“…To model the flow of water across a biological membrane, the following equation can be written from thermodynamic principles assuming that equilibria of temperature and pressure prevail between the intra-and extracellular media (Mazur, 1963;Toner et al, 1990b):…”

Non-ideal Solution Thermodynamics of Cytoplasm

“…The ideal model of the cytoplasm accurately represented this limited data for many of the cell types analyzed (i.e., the adjusted R 2 decreased when using the nonideal model), including HUVECs, TF-1 cells, porcine chondrocytes, human hepatocytes, human keratinocytes, 67 mouse oocytes, 68 porcine islets, 69 and hamster ova. 17 Also, with data obtained from hypertonic solutions only up 1.5 Osm/kg, the osmotically-inactive fraction did not change significantly with the modified Boyle van't Hoff equation and the osmotic virial equation.…”

Membrane Stability during Biopreservation of Blood Cells

“…Typically, there is a critical cooling rate for maximum survival. This cooling rate, however, varies greatly depending upon the cell type and is related to the cell-specific membrane permeability to water [21][22][23]. Freezing causes fluid-to-gel phase transitions affecting the membrane hydraulic permeability and the activation energy for water transport.…”