Membrane Permeability Characteristics of Metaphase II Mouse Oocytes at Various Temperatures in the Presence of Me2SO

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In this study, the hydraulic conductivity (Lp), Me2SO permeability (pMe2SO), and the reflection coefficients (ς) and their activation energies were determined for Metaphase II (MII) mouse oocytes by exposing them to 1.5 M Me2SO at temperatures of 30, 20, 10, 3, 0, and −3°C. These data were then used to calculate the intracellular concentration of Me2SO at given temperatures. Individual oocytes were immobilized using a holding pipette in 5 μl of an isosmotic PBS solution and perfused with precooled or prewarmed 1.5 M Me2SO solutions. Oocyte images were video recorded. The cell volume changes were calculated from the measurement of the diameter of the oocytes, assuming a spherical shape. The initial volume of the oocytes in the isoosmotic solution was considered 100%, and relative changes in the volume of the oocytes after exposure to the Me2SO were plotted against time. Mean (means ± SEM) Lpvalues in the presence of Me2SO (lMe2SOp) at 30, 20, 10, 3, 0, and −3°C were determined to be 1.07 ± 0.03, 0.40 ± 0.02, 0.18 ± 0.01, 7.60 × 10−2± 0.60 × 10−2, 5.29 × 10−2± 0.40 × 10−2, and 3.69 × 10−2± 0.30 × 10−2μm/min/atm, respectively. ThepMe2SOvalues were 3.69 × 10−3± 0.3 × 10−3, 1.07 × 10−3± 0.1 × 10−3, 2.75 × 10−4± 0.15 × 10−4, 7.83 × 10−5± 0.50 × 10−5, 5.24 × 10−5± 0.50 × 10−5, and 3.69 × 10−5± 0.40 × 10−5cm/min, respectively. The ς values were 0.70 ± 0.03, 0.77 ± 0.04, 0.81 ± 0.06, 0.91 ± 0.05, 0.97 ± 0.03, and 1 ± 0.04, respectively. The estimated activation energies (Ea) forlMe2SOp,pMe2SO, and ς were 16.39, 23.24, and −1.75 Kcal/mol, respectively. These data may provide the fundamental basis for the development of more optimal cryopreservation protocols for MII mouse oocytes.