Temperature dependence of mature mouse oocyte membrane permeabilities in the presence of cryoprotectant

Knowledge of cell membrane permeability characteristics facilitates the design of cryopreservation protocols which minimize damage from osmotic stress and reduce the incidence of intracellular freezing. Such permeability characteristics can be determined for oocytes from volume measurements taken during exposure to cryoprotectant. Individual mouse oocytes were held using negative pressure applied to the zona pellucida by means of a micropipet. Each oocyte was perfused with 1 ml 1.5 mol liter-1 dimethyl sulfoxide (Me2SO) or propane-1,2-diol at 30, 23, or 10 degrees C. The osmotic response of each oocyte before, during, and after perfusion was recorded by videomicroscopy until equilibrium was reached. Mean cell diameter across three axes was used to calculate oocyte volume, assuming sphericity, and, using mathematical modeling, values for hydraulic conductivity (Lp) were found to be 0.64, 0.41, and 0.20 micron min-1 atm-1 in the presence of Me2SO and 0.53, 0.36 and 0.15 in the presence of propane-1,2-diol at 30, 23, and 10 degrees C, respectively. Cryoprotectant permeability (omega) was 0.37, 0.16, and 0.035 for Me2SO and 0.43, 0.24, and 0.04 for propane-1,2-diol, while the reflection coefficient was 0.98, 0.94, and 0.99 (Me2SO) and 0.76, 0.99, and 0.95 (propane-1,2-diol) all at 30, 23, and 10, respectively. The corresponding activation energies (Ea) were 11.65 and 12.23 kCal mol-1 for Lp and 23.52 and 22.48 kCal mol-1 for omega, in the presence of Me2SO and propane-1,2-diol, respectively. Values generated for Lp and associated Ea were similar to those found for mouse oocytes in the absence of cryoprotectant, while omega and its Ea were similar to those found for oocytes of other species.