Permeability of the rhesus monkey oocyte membrane to water and common cryoprotectants

Successful cryopreservation of oocytes of the rhesus monkey (Macaca mulatta) would facilitate the use of this valuable animal model in research on reproduction and development, while providing a stepping stone towards human oocyte cryopreservation and the conservation of endangered primate species. To enable rational design of cryopreservation techniques for rhesus monkey oocytes, we have determined their osmotic and permeability characteristics in the presence of dimethylsulfoxide (DMSO), ethylene glycol (EG), and propylene glycol (PROH), three widely used cryoprotectants. Using nonlinear regression to fit a membrane transport model to measurements of dynamic cell volume changes, we estimated the hydraulic conductivity (L _p) and cryoprotectant permeability (P _s) of mature and immature oocytes at 23.5 °C. Mature oocyte membranes were most permeable to PROH (P _s = 0.56 ± 0.05 mm/sec) and least permeable to DMSO (P _s = 0.24 ± 0.02 mm/sec); the permeability to EG was 0.34 ± 0.07 um/sec. In the absence of penetrating cryoprotectants, mature oocytes had L _p = 0.55 ± 0.05 mm/min/atm, whereas the hydraulic conductivity increased to 1.01 ± 0.10, 0.61 ± 0.07, or 0.86 ± 0.06 um/min/ atm when mature oocytes were exposed to DMSO, EG, or PROH, respectively. The osmotically inactive volume (V _b) in mature oocytes was 19.7 ± 2.4% of the isotonic cell volume. The only statistically significant difference between mature and immature oocytes was a larger hydraulic conductivity in immature oocytes that were exposed to DMSO. The biophysical parameters measured in this study were used to demonstrate the design of cryoprotectant loading and dilution protocols by computer-aided optimization.