Permeability characteristics of human oocytes in the presence of the cryoprotectant dimethylsulphoxide

Equilibration of oocytes with cryoprotectants is a prerequisite of low temp erature storage. However, cryoprotectant exposure may induce damage via osm otic stress. Knowledge of cell membrane permeability characteristics and th eir temperature dependence would facilitate the design of cryopreservation protocols in which osmotic stress is minimized and the incidence of intrace llular freezing is reduced. To obtain such data, the volume change of donat ed human oocytes following exposure to cryoprotectant was measured at a var iety of temperatures. After removal of cumulus cells, each oocyte was place d in a 5 mu l droplet of phosphate-buffered medium. The oocyte was held in position by suction generated using a fine pipette and perfused with I mi 1 .5 mol/l dimethylsulphoxide (DMSO) at 30, 24 or 10 degrees C. The volume of the oocyte before, during and after perfusion was recorded by videomicrosc opy, Oocyte volume was calculated from radius measurements and the Kedem-Ka tchalsky (K-K) passive coupled transport coefficients, namely L-p (hydrauli c permeability), P-DMSO (permeability to DMSO) and sigma (reflection coeffi cient) were derived. The resulting coefficients were L-p = 1.65 +/- 0.15, 0 .70 +/- 0.06 and 0.28 +/- 0.04 mu m/min.atm; P-DMSO = 0.79 +/- 0.10, 0.25 /- 0.01 and 0.06 +/- 0.01 mu m/s and sigma = 0.97 +/- 0.01, 0.91 +/- 0.03 a nd 0.96 +/- 0.01 at 30, 24 and 10 degrees C respectively. The activation en ergy for L-p was 14.70 and for P-DMSO was 20.82 kcal/mol. The permeability parameters of human oocytes are higher than those of murine oocytes, sugges ting that they require a shorter period of exposure to DMSO with concomitan tly reduced toxic effects.