Membrane permeability characteristics of metaphase II mouse oocytes at various temperatures in the presence of Me2SO

In this study, the hydraulic conductivity (L-p), Me2SO permeability (P-Me2SO), and the reflection coefficients (sigma) 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 degrees 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 mu l 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) L-p values in the presence of Me2SO (L-p(Me2SO)) at 30, 20, 10, 3, 0, and -3 degrees C were determined to be 1.07 +/- 0.03, 0.40 +/- 0.02, 0.18 +/- 0.01, 7.60 x 10(-2) +/- 0.60 x 10(-2), 5.29 x 10(-2) +/- 0.40 x 10(-2), and 3.69 x 10(-2) +/- 0.30 x 10(-2) mu m/min/atm, respectively. The P-Me2SO values were 3.69 x 10(-3) +/- 0.3 x 10(-3), 1.07 x 10(-3) +/- 0.1 x 10(-3), 2.75 x 10(-4) +/- 0.15 x 10(-4), 7.83 x 10(-5) +/- 0.50 x 10(-5), 5.24 x 10(-5) +/- 0.50 x 10(-5), and 3.69 x 10(-5) +/- 0.40 x 10(-5) cm/min, respectively. The sigma 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 (E-a) for L-p(Me2SO), P-Me2SO, and sigma 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. (C) 1998 Academic Press.