THE INFLUENCE OF CRYOPRESERVATION ON MURINE OOCYTE WATER PERMEABILITYAND OSMOTICALLY INACTIVE VOLUME

Osmotic experiments were performed on unfrozen (N = 18) and cryopreser ved (N = 21) ICR murine oocytes in order to determine whether a standa rd cryopreservation process alters membrane water permeability (hydrau lic conductivity, L(p)) and/or osmotically inactive volume (V-b). Oocy tes, initially in an isotonic (288 mOsm) NaCl solution, were exposed t o 900 mOsm NaCl in a microdiffusion chamber. Cell size changes were vi deotaped and analyzed using a parameter estimation program. Best estim ates for a two-parameter model (L(p) and V-b) which includes the osmot ically inactive volume as a fitting parameter are presented for the fi rst time. The cryopreservation process produced no significant differe nce between the mean L(p) or the mean V-b values for the unfrozen cont rol population (L(p) = 0.64 +/- 0.15 mu m/min/atm, V-b = 24.7 +/- 2.9% ) and the cryopreserved population (L(p) = 0.63 +/- 0.12 mu m/min/atm, V-b = 28.0 +/- 10.8%). While the cryopreservation process did not cau se significant changes in the mean values of L(p), V-b, or the variabi lity of L(p), it did produce more variability of V-b. The cause of the increased variability of V-b produced by cryopreservation is unknown. These results suggest that the osmotic properties of unfrozen control oocytes can be used as a reasonable approximation for frozen-thawed o ocytes. They also suggest that multiple parameter models and parameter estimation methods may be useful in developing a more comprehensive u nderstanding of the more subtle alterations in osmotic properties that were detected here. Statistical tests were also used for the first ti me to confirm the assumption that all of the experimental populations were derived from normal distributions. (C) 1997 Academic Press.