EFFECT OF DEVELOPMENTAL STAGE ON BOVINE OOCYTE PLASMA-MEMBRANE WATER AND CRYOPROTECTANT PERMEABILITY CHARACTERISTICS

Knowledge of bovine oocyte plasma membrane permeability characteristic s at different developmental stages in the presence of cryoprotective agents (CPAs) is limited. The objective of this study was to determine the oolema hydraulic conductivity (L-p), cryoprotectant permeability (P-CPA), and reflection coefficient (sigma) for immature (germinal ves icle stage, GV) and in vitro-matured (metaphase II, MII) bovine oocyte s. Two commonly used cryoprotective agents, dimethyl sulfoxide (DMSO) and ethylene glycol (EG), were studied, Osmometric studies were perfor med using a micromanipulator connected to an inverted microscope at 22 +/- 2 degrees C. Each oocyte was immobilized via a holding pipette, a nd osmotically induced volume changes over time (dv/dt) were recorded. The L-p values for GV and MII oocytes in DMSO (L-p(DMSO)) were 0.70 /- 0.06 and 1.14 +/- 0.07 mu m/min/atm (mean +/- SEM) and in EG (L-p(E G)) were 0.50 +/- 0.06 and 0.83 +/- 0.07 mu m/min/atm, respectively. E stimates of P-DMSO for GV and MII oocytes were 0.36 +/- 0.03 and 0.48 +/- 0.03 mu m/sec, and P-EG values for GV and MII oocytes were 0.22 +/ - 0.03, 0.37 +/- 0.03 mu m/sec, respectively. The sigma values for GV and MII oocytes in DMSO (sigma(DMSO)) were 0.86 +/- 0.03 and 0.90 +/- 0.04 and in EG (sigma(EG)) were 0.94 +/- 0.03 and 0.76 +/- 0.04, respe ctively. These data demonstrate that bovine oolema permeability coeffi cients to water and cryoprotectants change after in vitro maturation. Furthermore, the bovine oocyte P-DMSO is higher than the P-EG. These r esults may provide a biophysical basis for developing criteria for cho osing optimal CPAs and for minimizing damage during addition and remov al of the CPAs. Additionally, these data support the hypothesis that d ifferent procedures may be required for optimal cryopreservation of di fferent oocyte developmental stages. (C) 1998 Wiley-Liss, Inc.